>>Another developer (currently on vacation) created a field (Claim) as an autoincrementing integer, to act as a primary key (the index itself is just a Regular, not Candidate). But now we are getting bad data, and the field values seemed to work okay for the first 25000 or so - and then reset to 1. So now there are are hundreds of bad records. So the last 800-odd records have duplicated claim numbers. The immediate question is, whether there is any way programmatically to determine what the next autoinc value is, and then how to reset it. The other question is how it got screwed up, and what to do to prevent it.
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>Update: The ultimate question is, is there any way to programmatically tell what the next autoinc value will be? That's probably in the header somewhere, if I could read it I could then know whether a fix was necessary and where to start.

Is it a free table or part of a database?

if the later, you can put insert into table into transcation, get the id and rollback it.