Just to add this tidbit.....and even though I've heard a dozen stories about this not happening, I just did chat with MS. This was the response.....
"So if we stayed at BLT for few days with dining, and then switch to Kidani without dining, the mug will still work?
Donna:
It would not, because it is length of stay for that first reservation, but it would work through the day of your check out from Bay Lake Tower at Disney's Contemporary Resort. You can, also, purchase refills and have them added at the point of purchase locations
You: ok, thank you. thanks for the help."
I wonder if the rules are changing.