I just returned from Kuala Lumpur via Hong Kong on CX yesterday. With my flight TO KL, I completed the AA Platinum Challenge and became PLAT (had been Gold). I called AA from KL to confirm the challenge completion and had my AA records updated, but did not think to contact CX in advance of leaving KL.

Long story and bad flights later, I realized that had been a major mistake. With a short layover in HK, I was not able to get into the beautiful CX lounge, (was it the WING), nor could I even convince the gatekeepers to let me board with the OW Saphires. Certainly, no recognition or quality treatment through the two flights.

So, the lesson is that if you're in a transition, don't assume anything, and press the matter quickly by making direct contact as soon as possible with the actual carrier, since they don't necessarily get updates and they won't even believe it if you show them your iPhone app indicating Platinum, etc.

Once I got to SFO, and to AA, the world changed and I was well-assisted by the Admirals Clubs reps who alertly moved me over to a delayed flight to Chicago and saved me four hours in the AC. (Unfortunately, the bags didn't make the switch - due I think, to very strange service in the transfer connections area of SFO outside of customs. That's a different story....)