Originally Posted by
javabytes
Are you a Medallion? If so, search for a full Y fare and see which flights say Upgrade Available. You'll still have to call to confirm, because complimentary Medallion upgrades and miles/SWUs/regional upgrades are different inventory buckets... but a flight that has inventory for Medallion upgrades is likely to have availability for miles/certs too, so it can at least be a starting point.
I would disagree. If there's no inventory for free upgrades (RU), there probably will not be inventory for instrument supported upgrades (RP), especially as the travel date approaches, but the converse isn't true. If anything, RP is a subset of RU IME. YMMV.
At first, this didn't seem to make sense, but RU upgrades are earmarked for elites (and their companions), while RP is available to anyone (with some miles).