Comparatives, Restatements and Errors

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Comparability is not created by adding a prior-year column at the end of the reporting process. It depends on stable definitions, consistent boundaries, controlled methods, retained source data and a documented change process. Sustainability metrics often evolve quickly: supplier coverage improves, emission factors change, models are refined, acquisitions alter the reporting entity and new topical standards introduce new datapoints. Without a controlled classification, every change can be presented as an 'improvement', every correction can be hidden as an estimate update and trend information can become misleading.

IFRS S1 addresses both ordinary comparative information and specific situations involving estimates, metric changes and prior-period errors. The first task is to classify the change. Only then should the team decide whether to revise a comparative, restate an error, disclose impracticability, preserve a forward-looking amount or explain a new methodology.

Unless another IFRS Sustainability Disclosure Standard permits or requires otherwise, IFRS S1.70 requires comparative information for the preceding period for all amounts disclosed in the reporting period. Comparative narrative and descriptive information is also required when it would be useful for understanding the current-period disclosures.

Narrative comparatives are not a requirement to repeat last year's wording. They are useful when the current description cannot be understood without knowing what changed, what remained consistent or how the current position compares with the prior period. A concise change explanation can be more useful than duplicating an entire governance or strategy narrative.

Figure 1. Decision tree for revised estimates, metric changes, new metrics and prior-period errors.

A metric amount can be an estimate. If new information provides evidence of circumstances that existed in the preceding period, IFRS S1 B50 generally requires the entity to disclose a revised comparative amount, the difference between the previously disclosed and revised amounts, and the reasons for the revision.

If an entity redefines or replaces a metric in the reporting period, IFRS S1 B52 requires a revised comparative amount unless it is impracticable, an explanation of the changes and an explanation of why the redefined or replacement metric provides more useful information. This is more than a methodology footnote: users need a comparable trend and a clear reason for the change.

A change in boundary, denominator, unit, factor set, calculation logic or classification can amount to redefining or replacing a metric if it changes what the metric represents.

A routine update to an input, such as a current-period emission factor within a consistently defined method, may instead be part of the normal estimate process. The entity should document the distinction.

A method change driven by a new Standard or amendment should identify the source, effective period, comparative transition and any impracticability provision.

Do not describe a change as providing more useful information without explaining how relevance or faithful representation improves.

When an entity introduces a new metric, IFRS S1 B53 requires a comparative amount unless it is impracticable. The term 'new' can arise because a newly material risk or opportunity is identified, a new topical ISSB requirement applies, the entity begins using a management metric or a disclosure gap is corrected. The reason does not automatically remove the comparative requirement.

The team should determine whether the prior-period data can be recreated from retained source systems or whether a reasonable estimate can be produced. If it cannot, document every reasonable effort and disclose impracticability. Avoid saying simply that the metric was 'not tracked' in the prior year; that fact alone does not establish impracticability.

A prior-period error is an omission or misstatement arising from failure to use, or misuse of, reliable information that was available when the prior disclosures were authorised and could reasonably have been obtained and considered. Material prior-period errors are corrected by restating comparative amounts unless impracticable.

IFRS S1 B58 requires disclosure of the nature of the prior-period error and the correction for each prior period presented, to the extent practicable. If correction is impracticable, disclose the circumstances and describe how and from when the error has been corrected. If the effect cannot be determined for all prior periods, restate from the earliest date practicable.

IFRS S1 defines impracticable as being unable to apply a requirement after making every reasonable effort to do so. A lack of convenient prior-year data, a costly manual reconstruction or a changed system does not automatically meet that threshold. The entity should document the attempts made, available alternatives, whether estimation is possible and the earliest date from which consistent information can be provided.

Search retained source systems, archives, consolidation files, supplier submissions and external datasets.

Assess whether a reasonable estimate can recreate the prior amount without inappropriate hindsight.

Determine whether only part of the comparative is impracticable and whether the remainder can be provided.

Record why further effort would not produce a faithful amount, not merely why it would be inconvenient.

Disclose impracticability specifically and state how and from when the new basis is applied.

Method changes can be driven by improved data, management decisions, new sources of guidance or amendments to IFRS S2. The December 2025 GHG amendments include specific transition requirements for entities that previously applied IFRS S2. In the first year of applying the amendments, preceding-period comparative information is adjusted for specified GHG method, Category 15, financed-emissions subtotal and industry-classification changes unless impracticable.

Narrative or descriptive comparative information is required when useful for understanding the current period. This is especially relevant when a process, governance structure, strategy, target or risk concentration has changed. The comparative should explain the change, not repeat generic prior-year text.

Figure 2. Correction workflow from issue detection to reconciled publication channels.

IFRS S1 specifies what sustainability-related financial disclosures should do when a material prior-period error is identified. It does not prescribe one universal operational process for replacing a published PDF, amending an XBRL filing, updating a regulator portal or issuing a website correction. Those mechanics depend on law, securities regulation, stock-exchange rules, filing taxonomies, assurance arrangements and the entity's publication policy.

Hypothetical scenario. In 2027, a manufacturer receives supplier information showing that a 2026 purchased-goods estimate used the wrong technology mix for circumstances that existed in 2026. The original method was reasonable based on information then available, and the supplier data were not reasonably obtainable before authorisation. The company revises the 2026 comparative estimate, discloses the difference and explains the reason under B50 rather than labelling the prior amount an error.

Hypothetical scenario. A group discovers that a controlled subsidiary was excluded from a 2026 energy metric because a consolidation mapping was not updated. The subsidiary's data were available in the ERP system and should reasonably have been considered. The issue is a prior-period error. If material, the group restates the comparative, discloses the nature and correction and remediates the consolidation control.

Hypothetical scenario. The entity replaces an employee-only incident-rate metric with a group metric covering employees and supervised contractors because the wider boundary better reflects a material operational risk. It recreates the prior-period comparative using retained records, explains the definition change and why the replacement metric provides more useful information. It also avoids presenting the new trend as though both published years had used the same definition originally.

Hypothetical scenario. A prior report disclosed a forward-looking range of transition expenditure based on information and plans available at that date. Actual policy developments later differ. The entity updates the current forward-looking range but does not revise the prior comparative using hindsight. It provides narrative comparative context explaining how assumptions and plans changed.