However, on this flight PE seemed to be either full or close to it. So... the block for over sale would probably extend “through” PE into J, right? FWIW, they were soliciting volunteers, and Y showed as “full” on standby, so there’s additional circumstantial evidence that Y was oversold.
A Y oversale will result in J seat blocking only if PE is also booked full. The app will often describe a cabin as booked "full" even in the absence of an oversale. You really need to look at the inventory figures, combined with the "booked" numbers to legitimately conclude there was an oversale of any cabin.
So... I can see a lot of opportunities for UA’s web coding team to make mistakes in the logic.
Yes, there were already concerns about whether the system was working properly with PE in the mix; now with PP they've totally broken it.