>>They'd better be, otherwise...As Jim Booth and Steve Sawyer pointed out in their "Effective Techniques..." book, not everything that we assume to be guaranteed to be unique are. The example they used is Social Security Numbers. There have been instances of duplicates among living persons.
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>My #2 kid went through much of his life using the wrong SSN. That would easily cause duplicates if the other person with that number happened to bank in the same place or use the same physician.

There are a number of things that we assume are unique. Unfortunately, while 99.99% they many be, that .01% can really cause a problem. If it ain't a 100%, then I don't want to deal it.< s >