Thanks for the clarification, MegatopLover. Also, what is Seatfinder? That must be a tool that has escaped my notice so far. Googling it allows me to book lots of seats at Broadway shows but none on airlines!
So ExpertFlyer does not let you look for 'O' class (no surprise). Can I infer, at the very least, that if a flight is showing P0 that there is no chance 'O' is available?