Originally Posted by
Teece
But that's what's being discussed here - the award seat is there, but you ALSO have to consider the cost of changing the underlying commercial fare. In this case, the original T class is no longer available, so changing to the more expensive W class is very pricey.
AFAIK, you don't need the underlying fare class to be available, only the award (upgrade class).
At long as there's U class available, you can change (on the phone), whether there is T class available or not, subject to the change rules/fees of the underlying T fare basis.