Originally Posted by
Paralytic
Are you sure you abandoned it? You actually checkin pretty soon in the checkin process - you don't have to go as far as choosing a seat or printing your boarding pass.
And, I've done a paid WT+ to CW upgrade at SFO before. I asked at checkin but they couldn't offer it there (but were aware of it) but did it in the lounge.
I definitely selected exit without checkin and the dire warning that you might loose any assigned seat (I didn't, which makes me wonder whether you checkin whatever you do!)
You're right about other upgrades, Y to WT+ and WT+ to J were on offer with a large display promoting them, but not J to F.