Closing a month freezes its reported figures a few days after it ends, so that a later change becomes a visible restatement instead of a silent edit.
Finance has always worked this way. Subscription metrics rarely do, which is why last quarter's MRR can differ the next time somebody looks.
The few days of delay let payments of the month's last days settle.
In sumwerk a month closes five days after it ends (you choose between 1 and 60). The API says which months are final.
A restricted, read-only key is all it takes. The first import runs in a few minutes; every number you see opens into the customers and Stripe references behind it.