Attendance was marked wrong — can it be corrected?

Yes. A school admin may correct attendance at any time from the tenant panel, and the correction repairs the pack consumption with it: the old consumption row is replaced rather than stacked, so the student's balance is right again without a manual adjustment.

Teachers themselves can only fill in attendance on the day of the session; outside that day the screen is locked and correcting becomes the admin's job. The history records who marked what, so "who took attendance here?" has an answer.