It used to be that P was a full-fare First Class fare bucket instead of F. Now it shows F and A as First buckets, but I do notice that sometimes it shows P nestled in the J fares. I assume it is a F fare, since it used to show P4 when all the J fares show 7 (on a not full flight). If my memory serves me, P *would* appear on a flight operated by a 777. F would appear in the past on a 777 operated flight that was sky cruiser seats or a 330/340 with the 'deep recliners'.