Classify principle, estimate, entity, or error

Five draft memos use the same heading: “Change in accounting.” Their facts do not belong under one answer.

Fact pattern	First route to test	Decisive evidence
Move between two acceptable inventory-cost principles for similar transactions	principle change	old and new principles, comparable population, required or voluntary basis
Warranty rate revised after new claims experience	estimate change	later information and support for the original estimate
Depreciation method changed as the expected consumption pattern changes	estimate effected by principle	asset benefit pattern, carrying amount, reason and preferability
Combined statements now include a different set of entities	reporting-entity change	precise reporting boundary and specialized-guidance exclusions
Signed year-end purchase contract was omitted from inventory cutoff	error	fact existed and should have been used when statements were prepared

Use exclusions, not keywords

For a principle change, ask whether the entity is moving between acceptable principles for comparable events. Initial accounting for a genuinely new transaction is not a change. Applying a different method to transactions that are substantively different need not be a change. Replacing accounting that was never acceptable is error correction.

For an estimate change, identify the uncertainty, original information set, later information or experience, carrying amount at the change date, and periods affected. A later outcome different from the estimate is evidence to analyze, not proof of error. Conversely, calling an overlooked contract “new information” does not make it new.

For a reporting-entity change, state exactly which entities' financial statements are now being presented. Do not place every acquisition, consolidation, disposal, or segment reorganization in Topic 250. The specialized transaction guidance can control instead.

For an error, name the origin: mathematical mistake, misapplication of GAAP, or oversight or misuse of an existing fact. Then identify whether recognition, measurement, presentation, disclosure, or several were wrong. Materiality does not determine whether an error exists; it informs the reporting response.

Separate cause from comparative appearance

Retrospective application and restatement may both create corrected-looking prior-year columns. Their messages differ:

retrospective application says the periods have been recast for a supported accounting principle or reporting-entity change;
restatement says previously issued statements contained an error; and
prospective application preserves earlier accounting because later information changed the estimate or because an authorized transition route begins from a defined date.

The note heading, opening-equity label, XBRL dimension, audit and filing handoffs, and communications must use the same cause. The route memo should include conditional logic where facts remain open rather than forcing a final label for scheduling convenience.

Route memo template

Write one page before opening the quantitative model:

Issue and affected population:
Old accounting and authority:
New or corrected accounting and authority:
Dated information timeline:
Classification and supplied professional conclusions:
Transition or correction route:
Affected statements and periods:
Tax, EPS, audit, filing, legal, control, and disclosure owners:
Open evidence and release stops:

That page is the root node of the whole package. Every number and disclosure must be traceable back to it; every unresolved classification fact remains visible until resolved.