It's possible that CAC engineers/workers simply wanted to wrap up a current phase of a project so they could be home for Christmas.
Nah, I agree with danielchin, probably more for Chun Jie, doubtful for Christmas.
Getting a few planes out rapidly and then doing some initial tests over the next couple of weeks means they can get home possibly a week or two early (if CAC let's them) before Spring Festival to beat the travel rush that will occur before February 8 next year.
Any guess when we'll see more than one J-20 in the air in the same shot?
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Probably a while to be honest -- we've got dozens of J-10B/Cs produced in the last couple of years, but I still don't think we have any pictures of two J-10B/Cs in the same photo.
This is because most of our photos are of aircraft taking and landing at manufacturing plants rather than at bases, where multiple aircraft formations are more common.
Also, the military typically does not release photos of new aircraft taken from the air until they have been in operation for a while. So I think it might be around 2018 or even later until we get a picture of multiple J-20s in the air in one photo... and such a photo will probably be Air Force released.