Room keys, slot cards, business IDs, grocery store cards... all of them can be re-programed. The theft ring may have found an easy way to snag cards, but any card can be made into a Credit/Debit card.

If the crooks wanted, they could use their own cards, with their own name, which wouldn't look suspicious and just program them over and over. It's just a magnetic strip like a tape recorder would use.

Here's a note which may or may not aply to the older door readers that Don mentioned.

Hotel card keys would, obviously, contain a "serial number" (to identify the individual physical card); a room number that the card is programmed to open; and the beginning and ending dates for which the card is valid.

The serial number part is interesting, if there is a sophisticated system in place. Someone comes back and tries the card in the door, two weeks later, and the computer kicks out the ID of the person who was originally issued that card.

I would think employee cards would be more likely to make use of that information. Who came in and who went out, even if the key code is the same for multiple persons.