I've heard that the Gamestop by me remove DLC cards from new games when they put them on the shelves and don't give them to the owners when they buy the game. Just a thought...
Stores are not supposed to open any of the boxes on sale. They are supposed to be sold sealed, and any box's placed on the shelves are either simple display boxes or are retail boxes still sealed but tagged so they cant be stolen. If a store is selling games opened, they are tampering with the product and should be taken to task for it. You paid for the entire contents of the box, if there is anything missing from the box it is the stores responsibility to replace any missing content.
So in short, get your pals to go back to the store and DEMAND the code and if they dont come across with them, report them to the BBB and also inform them that you will report them to the local police for fraud, false advertising, and tampering with a sealed product. Thats normally enough to get them to cough up what you are owed.
Best of luck.
Forza 1 / 2 / 3 / 4 Owner
Total Number of Unicorns across all games to date;
Zero, Nada, Zip, Zilch, Nix, Naught