I will give you wisdom in this matter! STAY AWAY FROM GAMESTOP!! I haven't bought anything from them for years! They have one of the most terrible costumer service I have ever seen!
Now I made my preorder my Bundle through Amazon and got an email on the day it was released and I happen to get it on the same day! Amazon has better Costumer service!
Now I can give you a suggestion Call Sony and give them the PSP barcode and they can link it gamestop( each barcode is assigned to a vendor: Amazon. Gamestop, Bestbuy etc) and since you haven't download anything yet they can give you a Code for the pr!eorder content that you are missing. They have records of what you download so it would be telling them the truth
I think that Gamestop puts its pre-order codes on the receipt when you pick up the game. otherwise, maybe they email it to you if you ordered it online.
when i went to pick it up the dlc code was on the receipt and if you ordered it online they will email you the code the day the game comes out.