Okay, when you click "unique" in a field definition, I assumed that FileMaker put a check on every change of that field such that its not possible to get a duplicate. NOT true!?!

So, where are all the loopholes? Or if its a shorter list... when does FMP bother enforcing that?

A quick check shows that FMP itself will violate the flag when auto-entering serial numbers. I assumed (wrongly) that it would continue incrementing numbers until it got one that was unique... but no, it happily corrupts its own databases. Pathetic.

So, it would seem the only way to guarantee a unique ID for a record is to use FMP's own ID... the CurrentRecordID. FileMaker guarantees that it is unique and will not change. Perfect.

Is there any other way to get that 'unique' guarantee other than using CurrentRecordID in one form or another?

Is there any reason not to create a calculation field "ID" = Status(CurrentRecordID) and index it and then use that as a matching field in Relationships?

Thanks.

That is ok, except that every Filemaker DB uses the same sequence of RecordIDs.