Unfortunately, Air China is the least reliable *A partner when it comes to honoring Mileage Plus award bookings.
There have been reports since 2014 of fully confirmed and ticketed segments being mysteriously cancelled with no warning or explanation:

http://www.flyertalk.com/forum/unite...ed-hacked.html

I wouldn't rely on Air China award tickets to get you where you want to go, no matter what the computer shows your booking to be now. You should have the Mileage Plus service center's # when you travel, and be prepared to get emergency rebooking assistance. Travel interruption insurance is also a must when flying award tickets on Air China.