The official word on this is that you can use the refillable mug you purchased only at the resort you purchased it at, and only for the length of the vacation you bought it on.
Of course there have been many people who were able to use elsewhere, and use on subsequent trips, but that is the official word, as I know it.
KathyFP, We do the same thing. Last year we stayed at AKL and bought the refillable mug, even though we stayed concierge and the beverages were included, and from Typhoon Lagoon.
We look at them as souvinirs that pay for themselves.