To wrap this up, all worked out well, I am BAEC Silver now. Hoping to hit Gold by Spring next year.

Got lounge access with my CX card all the time except at PVG. Agent printed the boarding pass and added the lounge information on it, but when I asked to change the FFP number to BA she printed a new boarding pass and did not scribble the lounge details on it.
As BA is using the MU lounge in PVG I didn't bother checking if the CX card would get me in and just had a snack and drink in one of the coffee shops.