Costs are discovered late all the time. A supplier increase appears on an invoice that arrives weeks after the shipment, a carrier surcharge turns up in a quarterly reconciliation, a rate card started on the first of the month while the paperwork was signed on the twelfth. The question is always the same: the cost really changed in March, you learned about it in June, so which months should carry it? Applying it from June leaves three months priced at a number that was not true. Applying it from March changes a closed period on purpose, and doing that safely is a matter of knowing exactly what moves and what does not.
- Set the effective date to when the cost really changed, not to the day you discovered it.
- Only the days from that date forward are re-priced; everything earlier keeps the value that was effective then.
- This is the one intended way a closed day changes, which is why the reason should be recorded.
- Discovering late is not the same as changing your mind: correcting a wrong value is an edit, not a backdate.
The default, and why backdating is the exception
Saving a cost normally closes the previous rule the day before and opens a new one from today, so nothing behind it moves at all. That default exists to protect history: a store should be able to look at March in June and see the same numbers it saw in April.
Backdating widens that window deliberately, and only as far back as the date entered. It is not a global recalculation and it does not touch anything before the date, which is what makes it safe enough to use without fear when the situation genuinely calls for it.
Three situations, three different answers
A price that really changed in March is a backdate: enter March, and March onward re-prices while January and February stay as they were. A value that was typed wrongly from the start is an edit to the existing rule, because there was never a period when the wrong number was true. And a price changing next month is an ordinary forward-dated rule, entered now with a future date so nobody has to remember on the day.
Confusing the first two is the common mistake, and it matters because they produce different histories. A backdate says the cost was one thing and then became another; an edit says the cost was always this and we recorded it incorrectly.
| Situation | Action | What moves |
|---|---|---|
| Price rose in March, found in June | backdate to March | March onward |
| Value was typed wrong | edit the rule | the whole period it covered |
| Price rises next month | forward-dated rule | nothing yet |
| Rule created by mistake | delete it | the gap is repaired behind it |
What to expect after you save
The affected days recompute, which means figures you have already looked at will move, and possibly figures you have already reported. That is the correct outcome, because the alternative is a history that is knowingly wrong, but it is also the reason to write down what you did and why.
The rule of thumb: any month that changes after it closed should have an explanation attached, and a backdated cost is the only explanation that ought to be available. If a month moved and nobody backdated anything, that is a question rather than a curiosity.
Keeping the paper trail
The most useful habit here is external to any tool. Keep a dated record of supplier quotes and rate cards, so the effective date you enter is a fact from a document rather than a reconstruction from memory, and the price list with effective dates is the shape that record wants to be in.
It also settles arguments later. A backdate that re-prices a quarter is far easier to defend, to an accountant or to a business partner, when the date came from an invoice rather than from somebody's best guess about when the increase probably started.
Telling people whose numbers change
If somebody has already seen the affected months, they should hear about the change from you rather than notice it. That is a one-line message: this cost rose in March, we learned about it in June, so March onward now carries the higher figure and the margins for those months are lower than previously reported.
It sounds like an admission and it reads as competence, because the alternative is a colleague or an accountant discovering that a closed quarter moved without explanation. A statement whose history changes silently is a statement nobody quotes twice.
The one thing not to do
Do not fold a late discovery into the current month to avoid disturbing the past. It is tempting, it keeps closed months closed, and it makes this month look worse than it was while last quarter keeps a margin it never earned. Every recognition date in a statement exists to put costs where they belong, and a deliberate exception made for convenience is the one that eventually makes everything else look negotiable.