Well if your mug is part of your
DDP then I would expect it to expire with your DDP credits - why would you expect it to still work at other resort when your dining plan has expired?
As to your second statement - refillable mugs are good for length of stay - if you are not staying at a resort that would suggest to me you cant buy a refillable mug for that resort (and why would you want to?) but if you are staying at that resort and you are staying 14 days then your mug would be good for 14 days.
I wondered if the point you may be trying to make might be why buy a mug which costs the same for a 3 day stay as a 14 day stay - that would be up to the person buying to do the maths and make their own choice.