The MVP Pennant Edition sets featured two styles - one die-cut, one regular. All cards were SN5000, but the first 500 were the die-cut. Thus, the die-cut cards have a SN out of 5000, but only a Print Run of 500. The regular cards have a SN5000 as well, but 4500 of them were printed, hence PR4500.
Side note for everyone - inserts do not have forums. Only the entire set has a Forum. Hitting the "Forum" link from an insert set still creates the post in the regular set forum, with no reference to the insert set in question.
I'll never quit collecting entirely, but I am downsizing. Check out my COMC store and help me thin out what I don't want so I can buy cards that I do want. See something you like? Send me a message on here, and we can knock the price down quite a bit. I'll even take a bit of a loss if it means getting you a card you really want.