The receipt has nothing to do with the items. When Bethesda offers "pre order" items they pack them in the box. In order to so many item codes straight they just pack item codes in the first batch. No receipts contain the codes to ensure you wont throw it away and that a mindless clerk wont have to be bothered with making sure you get it. I literally watched someone open the box on justintv its in there along with a skyrim advert.
It wouldnt be the first time I've been wrong, I just know how Gamestop and other dealers like to operate. Plus, its unlikely that Bethesda would spend the time and money making custom marketing, such as code cards, for each independant deal.
Its not impossible, just unlikely.