THe P and F fares would both be full fare first, correct? I am assuming that wouldnt show discount first? The flights I am looking at are both 757 from BOS-DTW-SEA. I am assuming the general rule of thumb applies, less trouble upgrading on the weekends versus business days? It looks like the cabin on NWA 757 is pretty big versus upgrades on CO or even my many Super 80 AA flights.
P= full-fare first
F= discount first
R= elite upgrades which apparently, theoretically, presumably, come as a subset of F.
NW has an equal or larger first class cabin than most domestic carriers, especially if you're comparing against a Super 80. Also consider that NW still flies lots of DC-9's with 16 FC seats on routes that other carriers have converted to RJs.
I would agree that some weekend flights (mostly Saturdays) allow for more upgrade opportunity than others. I suspect a Sunday DTW-SEA flight still has some serious upgrade competition.