Yes CX's systems will reply with a 2 week ticketing time limit once the booking is created, and CX segments will auto-cancel after that date. I don't know if it's unique to exCMB bookings or for all bookings. The AA oneworld liaison will usually attempt to extend the CX deadline to bring it in line with AA's. And it appears that CX has also blocked attempts by agents to circumvent the ticketing time limit by entering fake ticket numbers. When I set up the exCMB itinerary the AA GSA there was able to speak to CX on my behalf to extend their ticketing time limit once I've discussed payment with them.