Can I enter a cost change I found out about late?

Yes. Save the new cost with Effective from set to the day the change really started. The days from that date on are worked out again with the new value. Everything before it keeps the value that was true then.

A typical case: your supplier raised a unit cost on 1 March, and the invoice told you in April. Save the new cost with Effective from 1 March. nouz ends the old cost on the last day of February. It works out every order from 1 March again, even a March you already reported on. January and February stay exactly as they were.

The same works for a carrier's new rate card and a payment provider's new fee. For an overhead cost that started earlier than you entered it, change its Start date. One thing to know: saving from a date replaces every version of that cost that starts on or after it. On the Products, Logistics and Transaction fees pages, the panel names those versions before you save.

This is the one intended way a closed month changes, so do it on purpose. A month that moved should always have a reason, and a backdated cost carries its reason in its own start date.

If the old value was never right at all, a typo rather than a price change, edit the rule instead. That rewrites it for all its days. To see what a cost change would do before you commit, try it in the Forecast's What if. It prices the months ahead without touching your history.