I don't have any idea of how often this happens but I have seen at least one instance of a bat being used nearly two years after the stamped date. Not one of my bats and I only saw pictures of the bat and the picture it was photomatched to. Typically, I would have to say the bat gets used with in a two weeks to six month range. IMHO.

If the bat has any distinguishable use marks then I would go look on Getty Images from the date of manufacture to see if I could photomatch it. If you can then you would have a definitive answer.