When I went to college over 20 years ago, they university used SSN as the student number (this has now changed). We had about 25,000 students on campus. I know of two people in that 25,000 that had the same number. Neither knew about it until they got to college. It caused a big mess, but was eventually straightened out.


>I agree that an SSN should not be used as a PK, but it should be unique. If someone else uses the same SSN as you, your wages are reported incorrectly and there will be trouble when you retire. If the same SSN is used for more than one individual, it should be reported. The SSN Administration now sends out contribution statements annually and if someone does not receive one, then they need to contact the SSN to get it straightened out. In the majority of cases, duplicate SSNs exist due to identity theft (typically from illegal aliens making up an SSN to get employment more often than actual identity theft) and only a very small number are due to the administration actually issuing duplicates. When that happens, it is usually because the SSN thought the original holder of the SSN is deceased. Also, an SSN is typically required to get a job (not necessarily verified though and except for some visa circumstances) and in the financial world, a SSN is now required for financing.
> It is due to Homeland Security's Sarbane Oxley Act of 2002. If you finance your auto insurance you have to have either an SSN or an ITIN (individual taxpayer identification number). Also for financing school loans, purchasing weapons, and getting a commercial driver's license. Smaller businesses are still trying to comply with the Sarbanes-Oxley Act but most larger organizations have already met the requirement.
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