A period you can still edit is not closed

Closing a period is a claim: these numbers are final, and anyone relying on them can. That claim is only worth something if the numbers cannot subsequently change.

What locking actually prevents#

A lock stops new postings dated inside the period. It does not stop you fixing things; it changes how you fix them, from editing history to posting a correction in the open period.

That distinction is the whole point. An edit changes what the statements said without leaving evidence that they changed. A correction leaves both facts on the record: what was originally booked, and what was done about it.

Corrections go forward#

Find an error in a closed period and you post a reversal and a re-posting, both dated now:

Account	Debit	Credit
6100 · Rent		2,400.00
2100 · Accounts Payable	2,400.00
Total	2,400.00	2,400.00

Then the correct entry is posted normally. Three entries now exist where a mutable system would show one — and that is the desired outcome. The ledger reads as a narrative: this was booked, this was wrong, this is the fix.

Both entries stay in the books and net to zero, so every report that includes them is unaffected in total while the history remains complete. Comma enforces this rather than requesting it: a posted entry is never edited, a correction is one linked reversal that swaps every side, and the original is marked reversed rather than removed.

When the error is material#

Not every correction is a simple reversal. If a closed period was wrong by an amount that would change someone's decision — a lender's, a shareholder's, a tax authority's — correcting it silently in the current period is not enough. Comparative figures may need restating and the change disclosed.

The bookkeeping mechanism is the same. What changes is who needs to be told. Materiality is a judgement, and it is the kind worth writing down at the time rather than reconstructing later.

Who can unlock, and why it should be awkward#

Some systems allow reopening a closed period. Sometimes that is genuinely right — a period closed prematurely, before the last invoices arrived.

But reopening should be deliberate, restricted, and logged. If anyone can unlock any period at any time, the lock is decoration. The useful design makes reopening possible and visible, so it happens when it should and leaves a trace when it does.

What closing gives you#

Comparability. Last March means the same thing today as it did in April, so month-on-month comparison is real rather than an artefact of who edited what.

Accountability. Someone asserted the numbers on a date. That is what a sign-off is.

A workable audit. An auditor testing a period needs it to hold still. A period that moves during fieldwork means starting again.

A shorter close next month. Locked periods cannot be reopened by accident, so this month's work stays this month's.

The close sequence is the fifteen steps that get you to the lock, and the checklist template is that sequence in a form you can hand to someone else. The immutable ledger post is the longer argument for why the lock has to be real.