Incomplete supplier data does not automatically prevent ISSB reporting. When information cannot be measured directly, IFRS S1 allows companies to use reasonable estimates and explain how they were calculated. For Scope 3 emissions, IFRS S2 requires a credible measurement method, supportable assumptions and clear disclosure of data quality and uncertainty.
The key question is not simply whether to estimate or leave the information out. You need to determine which available data best represents the activity, whether the information is material and whether the calculation can be reviewed. A supplier’s failure to respond creates a data gap that must be managed and disclosed. It does not automatically remove the reporting requirement.
What does ISSB reporting require when supplier data is missing?
The ISSB issued IFRS S1 and IFRS S2 in June 2023. Both standards are effective for annual reporting periods beginning on or after 1 January 2024, although jurisdictional adoption, local law and transition relief determine whether and how a particular company must apply them.
IFRS S1 addresses material sustainability-related risks and opportunities that could reasonably be expected to affect an entity’s prospects. Information is material when omitting, misstating or obscuring it could reasonably be expected to influence decisions by primary users of general purpose financial reports. IFRS S2 applies that investor-focused framework to climate-related risks and opportunities, including disclosure of Scope 1, Scope 2 and Scope 3 greenhouse gas emissions.
Start with the disclosure requirement and materiality, not with the supplier questionnaire. If a supplier-data gap affects a material amount or explanation, leaving the field blank can obscure the underlying risk. Your reporting team should identify a suitable measurement method, retain the supporting evidence and explain significant uncertainty. If the gap does not affect material information, document that conclusion rather than treating non-response as the reason for exclusion.
As of October 2026, the ISSB has also issued targeted amendments to IFRS S2 that become effective for annual periods beginning on or after 1 January 2027, with early application permitted. Those amendments address specific greenhouse gas measurement and financed-emissions issues. They do not remove the core Scope 3 measurement framework discussed in this article.
When can you use estimates or proxies for ISSB reporting?
IFRS S1 states that the use of reasonable estimates is an essential part of preparing sustainability-related financial disclosures when amounts cannot be measured directly. An estimate does not become unreliable merely because it contains uncertainty. Its usefulness depends on whether the method is appropriate and whether the estimate and its uncertainty are accurately described and explained.
For Scope 3 emissions, IFRS S2 requires the use of all reasonable and supportable information available at the reporting date without undue cost or effort when selecting the measurement approach, inputs and assumptions. The standard’s measurement framework recognizes that companies may need secondary data when primary information from a specific value-chain activity is not available.
The ISSB’s implementation FAQs make the boundary clear: a company cannot ignore known information or fabricate a number, and it does not have to conduct an exhaustive search. The evidence and effort that are reasonable will depend on the company’s circumstances, resources, experience and the importance of the information.
A defensible estimate should pass four tests
· Relevance: The input represents the product, service, activity, technology, geography and reporting period closely enough for the intended disclosure.
· Supportability: The source, method and assumptions have an appropriate basis and can be explained to a reviewer.
· Consistency: The method is applied consistently across comparable activities and periods, or changes are identified and justified.
· Transparency: The disclosure explains significant assumptions, data characteristics, limitations and measurement uncertainty.
These tests are practical controls, not a substitute for reading the standards or applicable local requirements. A technically correct formula can still produce a weak disclosure if the input does not represent the activity or the evidence trail cannot be followed.
Which supplier-data inputs should you prioritize for Scope 3?
IFRS S2 does not say that every supplier-specific input is automatically better than every secondary input. It requires a company to prioritize data that best represents the value-chain activity and to consider characteristics including technology, jurisdiction, timeliness, activity specificity and verification. The decision should reflect both relevance and quality.
| Input | When it can help | Control question |
| Supplier-specific primary data | When the supplier can provide activity-level or product-level data for the relevant period and boundary | Is the method, boundary and source evidence complete enough to use? |
| Hybrid data | When supplier activity data can be combined with suitable secondary factors | Are the primary and secondary elements compatible and clearly distinguished? |
| Average activity data | When physical quantities are known but supplier-specific emissions are unavailable | Does the factor match the material, process, technology, geography and period? |
| Spend-based data | For screening, prioritization or where more specific data is not feasible | Are currency, price year, inflation and economic-sector assumptions controlled? |
| Prior-period or proxy data | When it remains representative and no better current input is available | What changed in the supplier, site, process, energy mix or reporting boundary? |
The GHG Protocol Scope 3 Standard and its calculation guidance describe supplier-specific, hybrid, average-data and spend-based methods. For purchased goods and services, the correct choice depends on the reporting objective, data availability and the quality of the available input. More specific data is not automatically more accurate if its boundary, method or source is weak.
VECTRA’s guide to FMCG sustainability data and supplier evidence provides a practical example of prioritizing primary data where it can change a decision, rather than asking every supplier for the same level of detail.
How should you document an estimate?
A defensible estimate needs a reproducible evidence record. The record should allow a competent reviewer to understand what was measured, which source was used, how the amount was calculated and why the method was reasonable at the reporting date. That reviewer test is a practical control, not wording taken directly from the standards.
1. Define the disclosure, activity, supplier population, reporting boundary and period.
2. Record the original data source, owner, extraction date and any transformation applied.
3. Identify the measurement method, factor, conversion rule and calculation formula.
4. Explain why the selected input represents the activity better than the available alternatives.
5. Record assumptions, exclusions, data-quality limitations and sensitivity where relevant.
6. Name the preparer, technical reviewer and approver, and preserve the review evidence.
7. Set a trigger for reassessment when new supplier data, a changed method or a changed activity becomes available.
If new information provides evidence about circumstances that existed in the preceding period, IFRS S1 paragraph B50 may require revision of the comparative estimate, subject to the standard’s impracticability provision. Keep the version history and the reason for any revision so the reporting team can distinguish a correction of prior information from a change caused by a new-period event.
A simple worked example
Assume a manufacturer purchased 800 tonnes of steel during the reporting period. The supplier did not provide product-level emissions data. The company selected a cradle-to-gate secondary factor of 2 tonnes of CO2e per tonne because it matched the material, technology, geography and factor year more closely than the other available sources. The estimate is 1,600 tonnes of CO2e.
The calculation alone is not enough. The file should retain the purchase quantity, factor source and version, applicable boundary, unit conversion, selection rationale, verification status, known limitations, reviewer approval and a plan to seek more representative data. The factor in this example is hypothetical and is not an industry benchmark.
What must you disclose about methods, inputs and uncertainty?
IFRS S2 paragraph 29(a)(iii), together with paragraphs B55–B56, requires information about the measurement approach, inputs and assumptions used for greenhouse gas emissions. For Scope 3, the disclosure must help users understand how the company prioritized the highest-quality data available and the extent to which the measurement uses inputs from specific value-chain activities and verified inputs.
IFRS S1 paragraphs 77–81 address measurement uncertainty. A company identifies disclosed amounts subject to a high level of measurement uncertainty and explains the sources of that uncertainty and the assumptions, approximations and judgments used to measure them. Depending on the nature of the amount, useful information can include sensitivity to methods or assumptions, the expected resolution of uncertainty and changes made to past assumptions.
For each material estimate, prepare to explain:
· what was estimated and why direct measurement was not available;
· which method, source data, factor and assumptions were used;
· why those inputs were relevant to the activity and reporting boundary;
· how much of Scope 3 used activity-specific or verified inputs;
· which limitations create significant measurement uncertainty;
· whether a reasonable alternative assumption would materially change the amount; and
· what changed from the prior period and how the comparative information was treated.
Do not turn the disclosure into a data inventory. Focus on information that a primary user needs to understand the amount, the uncertainty and the decisions made in preparing it.
Can missing supplier data justify leaving Scope 3 emissions out?
A missing supplier response, by itself, does not justify omission. IFRS S2 paragraph B57 presumes that Scope 3 greenhouse gas emissions can be estimated reliably using secondary data and industry averages. In the rare case that an entity determines estimation is impracticable after making every reasonable effort, it discloses how it is managing those emissions.
This is a high threshold, not a shortcut for low questionnaire response. Your team should first test the available activity records, secondary sources, proxy methods and reasonable effort required in the circumstances. The conclusion and effort should be documented. The precise application may also be affected by transition relief, jurisdictional adoption and local requirements.
Do not confuse this Scope 3 provision with IFRS S1’s limited relief for quantitative disclosure of current or anticipated financial effects in specified circumstances. The reliefs address different requirements and should not be treated as a general permission to omit climate information.
Who should own supplier-data estimates?
Incomplete supplier data is not solely a sustainability-team problem. Finance, procurement, sustainability, reporting, risk and internal control teams should have defined responsibilities so material estimates are consistent, challenged and approved.
| Team | Primary responsibility | Evidence retained |
| Procurement | Coordinate supplier requests and confirm commercial and activity records | Requests, responses, purchase data and escalation record |
| Sustainability or climate | Select the method, factors and data-quality criteria | Method paper, factor source, calculation and limitations |
| Finance or reporting | Assess materiality, comparatives and disclosure consistency | Review notes, disclosure mapping and approval |
| Risk, compliance or internal control | Challenge assumptions and test whether controls operated | Control test, exceptions and remediation record |
| Management owner | Approve significant judgments and unresolved limitations | Decision, rationale and sign-off |
How can you improve supplier data without delaying the report?
The objective is not to eliminate every estimate immediately. It is to improve the estimates that could materially affect the disclosure and to reduce uncertainty over time. A controlled improvement plan can run alongside the current reporting cycle.
· Prioritize estimates with the highest potential effect on the disclosure, not simply the largest number of missing supplier fields.
· Ask suppliers for a defined record, boundary, period and method instead of sending a broad request for ESG data.
· Reuse evidence across reporting frameworks only when definitions, boundaries and control requirements genuinely align.
· Track whether a better input would change a decision, reported amount or explanation before adding another data request.
· Reassess the estimate when a supplier changes its site, process, energy source, product specification or ownership, or when a better factor becomes available.
Use VECTRA’s supplier engagement guide to make each request decision-led and evidence-specific.
For reporting teams managing overlapping requests, the guide to reducing ESG data fatigue across reporting frameworks explains how shared definitions, controls and source records can reduce duplication.
Teams that need a structured capability-building resource can also use VECTRA Marketplace’s course on collecting reliable ESG data, which covers supplier data gaps, governance, verification and audit readiness.
Start here before the next reporting sign-off
Select the three supplier-data estimates with the greatest potential effect on a material disclosure. For each one, record the boundary, source, method, assumptions, verification status, uncertainty, reviewer and next improvement action. Then compare that record with the draft disclosure. If a user cannot understand why the number is reasonable and where it remains uncertain, the file is not ready for sign-off.
VECTRA’s Reporting service helps organizations align reporting frameworks, strengthen data collection and performance monitoring, assess gaps and improve the controls supporting sustainability disclosures.
Where the intended users or claims require a separate confidence check, VECTRA’s Independent Quality Assurance service can review the evidence, method and reporting conclusion against an agreed scope.
Frequently asked questions
Can you use estimates in ISSB reporting?
Yes. IFRS S1 recognizes that reasonable estimates are essential when amounts cannot be measured directly. The method must be appropriate, the process must be free from material error, and the estimate and significant uncertainty must be accurately described and explained.
What if suppliers cannot provide Scope 3 emissions data?
Use the most representative reasonable and supportable inputs available under IFRS S2’s Scope 3 measurement framework. Depending on the facts, that may include hybrid, average activity, spend-based or other secondary data. Explain the method, assumptions, data characteristics and limitations.
Does supplier-specific data always take priority in ISSB reporting?
No. Activity-specific and verified data are important characteristics, but the input must also faithfully represent the relevant technology, jurisdiction and period. Weak supplier data can be less useful than well-matched secondary data.
What is measurement uncertainty under IFRS S1?
Measurement uncertainty arises when an amount cannot be measured directly and must be estimated. For amounts subject to a high level of uncertainty, disclose the sources of uncertainty and the assumptions, approximations and judgments used.
Do you have to disclose every supplier data gap in ISSB reporting?
No. Apply the materiality requirements and the specific disclosure requirements. Document non-material gaps internally, while disclosing information users need about material estimates, Scope 3 input characteristics and significant measurement uncertainty.
View related posts
· ESRS Reporting for Non-EU Companies: Are You in Scope of ESRS-40a?
· Closing the 5 Hidden Data Gaps in ESRS Reporting for CSRD Readiness
· Audit Assistance for Mandatory ESG and Climate Disclosures
VECTRA International is a trusted Business Resilience & Operational Capability Building Partner. Through our ecosystem of integrated solutions, we help organizations transform operational complexity into resilient performance, measurable business impact, and sustainable growth.
Chaussée de Wavre 1517B, 1160 Brussels, Belgium.
A Note on Our Visuals: At VECTRA, we combine human expertise with advanced technology. Some of the supportive imagery in this article was generated using artificial intelligence tools like Google Gemini. We ensure all conceptual AI assets align with our brand standards and accurately reflect our data.
