FWIW, I flew AA PIT to ORD, then CX ORD HKG MNL about a year ago on separate PNR's, I asked at AA PIT checkin if they could check my bags all the way through to MNL, they asked for proof of my CX ORD HKG MNL flight, I showed it, and they booked the luggage all the way through to MNL for me. I flew F PIT ORD, then Business ORD HKG MNL, not sure if that made any difference or not.