I am headed to Asia this month and trying to plan the trip so as to maximize my chance of a SWU from Y to C. I typically book all of my travel on united.com and tell the search that I will be using a systemwide uprgrade.

Some of the itineraries that are suggested say "Upgrades may be available." What is interesting is that for some of these itineraries where United is suggesting that an upgrade is available are actually C0, and some of the itineraries where they say there is no upgrade available are > C4. Is there any rhyme or reason here?

And why are all of the business seats out of Asia into North America the weekend of June 26 sold out of paid C??