I was thinking about this and wondering where to look what fare I purchased. The receipt does not state it.

But if I go to My Trips, then manage Reservations, then View Current Reservation, I can see that for my next trip to PVG, my Fare Class is United Polaris Business (P).

Most probably, the OP's one would have said United Polaris First (A). The key word being "First".

In a sense, the problems caused by the elimination of a seat class is the same as the problems caused by the introduction of a seat class. When they announced the introduction of Premium Economy, I asked in that thread how would I be sure that I get the seat in Premium Economy that I purchased. I was told that there's no way it would happen that I would find myself in Economy +. This thread convinces me that I was right to worry. And the pain of being in Economy + instead of Premium Economy on a 16 hours flight is greater than the pain of being in Polaris Business rather than in Polaris First.