Locking the period

Every section ends with a sign-offCloseSign-offFormal approval that a section is complete by someone other than the person who prepared it. That's segregation of dutiesControlsSegregation of dutiesSplitting authorization, recording, custody of assets and reconciliation across different people, so no one person can both commit and conceal an error or fraud — at minimum, preparer ≠ approver. Whoever can post to cash shouldn't be the one who reconciles it. The sign-off, the preparer, the reviewer and the time all go into the audit trailControlsAudit trailThe immutable record of every state change.

When every section is signed off, the periodCore ledgerPeriodA fiscal reporting window is closed and postingCore ledgerPostingCommitting an entry to the ledger, making it immutable to it stops. That keeps reported numbers stable: someone reading September's statements in March sees the same figures the signer saw. An error found later is never fixed by reopening the locked books. How it's corrected depends on how much it matters, judged under ASC 250 and, for SEC registrants, SAB 108 (which also asks whether fixing it in the current period would misstate the current period). An immaterial error becomes an out-of-period adjustmentCloseOut-of-period adjustmentCorrecting a prior-period error in the current period, permitted only when the error is immaterial to both periods in the open month. An error material to statements already issued is corrected by a restatementCloseRestatementRevising previously issued statements to correct an error material to them ("Big R") — comparatives are relabeled Restated and the error disclosed: the prior period is reissued, openly, with the error disclosed. The in-between case, immaterial to the old period but too big to absorb in the new one, is a revisionCloseRevisionCorrecting an immaterial prior-period error that would be material if corrected in the current period by adjusting the comparatives ("little r") — labeled As revised, no reissuance of the comparatives.