Not sure why the GAs were saying that STT isn't eligible for upgrades. Just because it's "international" doesn't mean you can't get elite upgrades. I've taken that flight and it's domestic FC service, and it is clearly stated that flights to the Caribbean are eligible. Also, just because a plane has B/E seating doesn't mean you can't get upgraded on a domestic segment. A good example is when the 777 flew from ATL to LAX and then on to SYD. If you had a domestic reservation as far as LAX and are lucky enough to get the 777, you are eligible for a medallion upgrade. My boss got upgraded on that flight at least once.