Originally Posted by
Bonehead
Just checked in my 1K SO for her SAN--SFO flight and upgraded her for $149 (only 2 seats left, so Mr. Wonderful took care of any uncertainty).
She's now in P, so it definitely didn't restrict the search to Y/B/M.
That's almost certainly an UP/UPDI that books into P. The difference between Y and F on that route on a medium priced fare (i.e., a Q or H) is often just tens of dollars.