The band is not your room key in the traditional sense. YOU have entitlements to open the room. Your magic bands are all associated to YOU.
The door scans the magic band being used, the system looks up who that band is registered too. if they have a valid reason to enter that room, access is granted. It is all part of a relationship database. No info is stored in your magic band about you or your entitlements.
If, like me, you have 20 magic bands, every one of them will open your room. That is why it is a good idea to deactivate any bands you have lost, or know you will not use any ore.
We take 1 band to use, and have one as a back up per person in case it is lost. The rest form a nice daisy chain hanging from the closet rod in our home.