Thanks - I had specifically wanted to avoid this scenario because I prefer to have my MPC number on the record because I'm travelling Y and I tend to get upgraded a lot on long haul, probably on more than half my long haul flights. Don't want to lose out on that.

Instead, I'm flying an extra roundtrip HKG-BKK-HKG in Y to make up the 2K miles I need so I can qualify predictably based on 100% CX flights (which always post 2-3 working days after the flight), and all my AA flights will be in my new Gold membership year, so then I don't have to care about when the miles post.

OT: Although AA sucks as an airline in pretty much every way an airline can suck, it's great for earning Club Miles because pretty much any revenue fare will give you 100% Club Miles.