I don't think there are even dates stored on the room keys. I've extended my stay in the past and they just enter my new departure date in the hotel computer and my card continues to work. All they would need would be a number on the mag stripe that relates to your hotel stay on the computer. Never any need to store any personal information. However, I've never spoken to any systems people about what exactly is stored; just seems that other than a guest number, there's no need for anything else.