journey availability makes it weirder...
I currently have a reservation on Nov 6th, BOS-UA749-IAH-UA1249-SJC.
If you search, UA1249 has R=1. But full journey availability shows R=0. That's true even if you do a search for a new reservation from BOS-SJC, even using "mileageplus upgrade awards", it doesn't show UA1249 as upgradable.
I can't conceive of how this happens. Are upgrades processed per journey or per segment? I don't get it.