Posted By:
Scott ForrestDo all of your business cards have a similar look and feel to one another? He might very well have consumed other products that had different cards enclosed, but maybe he decided to keep those "un-stamped" and dump all the E104's as business cards. It's also possible that the other cards in his collection already had ads stamped on the back (if he was even a collector - perhaps he was just a consumer of the product).
I don't think there's anything at all strange about this.