Is it possible to return Wikipedia API data giving a user's edit count or group membership (flag) data for a specific date, rather than for the current time?
Re counts, I'd like to be able to query for a given user's edit count up to a cut-off date time in the past.
Re flags, user account logs tend show the removal of a flag (sysop, bot, etc.) but often the initial grant of the flag is not logged. However, to be removed it must have been granted and I'd like use API calls for past times to try and find the date-time of grant.
The documentation/worked examples aren't of help in trying to assess if this is possible.
It is not possible via the API. You could reconstruct it from publicly available dumps and event logs but it's a lot of work.
The MediaWiki edit history dataset includes such reconstruction. At some point it will be made publicly available; right now only researchers can get access on an individual basis.