What policies should govern versioning of emission factors within a carbon ledge

Adopt semantic versioning for emission factors (major.minor.patch) and require every ledger entry to lock the factor ID and version. Major updates reflect methodological changes (e.g., new GWP values or system boundaries) and trigger disclosure and potential restatement; minor updates reflect dataset refreshes (time/region specificity); patch updates correct errata without methodological impact. Store factor provenance (publisher, methodology, publication date, URL), applicability (scope, region, sector), and expiry/review dates. Implement effective-dating so posting logic selects the correct version for the activity period. Provide a governed remeasurement process: quantify impacts, document rationale, and post adjustments rather than overwriting historical factors. Align with IPCC guidance on methodological consistency and document changes per assurance standards (ISAE 3410). For electricity, distinguish grid-average vs. market instruments and reference authoritative datasets (EPA eGRID, national inventories). Automate alerts for expiring factors to prevent stale data usage. Key Takeaway: Lock factor versions to entries, effective-date selection, and adjust via governed remeasurement—never overwrite historical factors.