Originally Posted by
olouie
… U space has to be available or you get downgraded back into Econ then wait for upgrade processor to run.
this is correct … I’ve dealt with this multiple times on SEA<>LAX, where riding in the back for 2+20 isn’t that big a deal, but would most likely not entertain it on a TCON (esp since I *think* your original date of purchase — which impacts UG list position — doesn’t pull through to the new flight)