Corrected entry: The actual average "shelf life" of a piece of U.S. paper currency is about 18 months. But the action in this movie is supposed to take place over a few years. During that time, the $5.00 bill with Jon's name and number on it almost certainly would have been pulled from circulation and destroyed due to normal wear and tear; in fact, if it ended up in a bank's inventory and the "mutilation" were discovered, it almost certainly would have been pulled even sooner.
wolfchild
19th Sep 2003
Correction: There are many explanations to this. The money really just needed to be out of circulation for some reason or another, for a while. I just recently sent out over three dozen bills back into circulation that I had had in a box for almost 10 years. And I also once found a $20.00 bill in the inside pocket of a fairly old jacket that I got at a thrift store. So, there are definitely ways that the bill could have remained/made back into circulation, and given the nature of the film it would have taken one of those routes.
wolfchild