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It used to be that the first three digits of an SSN indicated the office, or anyway region, that issued it. Once, when I wished to see whether we had any SSNs masquerading as properly meaningless IDs, I searched a dataset for IDs that a) were nine digits long, b) began with the same three digits as mine, and c) belonged to an Ohioan. Of course there was one organization that hadn't got the word.
This style of issuance may have changed since--I got my Social Security card sixty years ago--but it does reduced the search space.