[Crazy Jetty]

There are a few reasons. As most everyone has said, revisions is the number one reason.
But sometimes stock crew will stock newer cases to the shelves, leaving older cases behind, which will sit in the backroom for a few months, continuously passed over, until someone grabs it and gets it out for inventory. That would be the number two reason.

Sometimes a simular situation where a case will sit in the warehouse or distribution center, getting passed over for a few months, and then finally gets shipped out to a store. I'd say that's probably the third biggest reason for older toys to show up.