Originally Posted by
MSPeconomist
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).
Not sure I said anything different. If RP is a subset of RU - or if not a subset, then at least correlated - then if you can find RU, your chances of finding RP on that flight are higher than if you didn't find RU on that flight.