Index on collector tag collector unique

Strange behavior I've never seen before I have a 3 character field called collector.    I have many records with collector= '31' .   When I index using the command "Index on collector tag collector unique"   I get every one except collector 31.   I get collector 3, I get collector 30, but I don't get collector 31.   There are over 2000 records with collector = '31'

I realize you have to reindex every time to make sure you have every collector accounted for, so it's not that

This is really odd.

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