I'm confused too. For example I bought a webfare on Orbitz ORD-SEA-ORD for the Jul. 4th weekend. It was booked in "T" class. T class is not upgradeable with an SWU but is with a North America Upgrade. At check-in in SEA they told me it was not upgradeable at all. But later another gate agent let me upgrade with 500 mile certs. and gave me a first class boarding pass on the spot. Go figure. I guess it just depends on who you speak to.