Originally Posted by
Finkface
I think that's probably it as well. Or he was looking at the wrong U, by choosing to look at all upgrades, not just the one specific to his status level.
There is only one U. The different in "U"s you are seeing is for different upgrade avenues [MVP via Y/YAS fares, Golds via H+, Mileage, and Guest Upgrade], but they all book into the same U bucket. If U is not available for Guest Upgrade Certificates, then the Gold U or the Teal U will not be available as well. So, if a Gold sees the Gold U then an MVP will see a teal U, both of them can confirm the upgrade as early as booking. Since the OP is a Gold, the OP is eligible to upgrade via all avenues granted he meets certain fare class criterias for each upgrade avenue.
Bottom line, if you see the slashed U next to the flight information in the flight search, there is no U available.