Looking at the wording on these cards I'm guessing that you can't use Chewie's pilot ability to flip a face up damage card face down again if that card has been flipped face up using Artoo's ability.
That's a bit of a mouthful - maybe I can illustrate it better.
At the end of the end phase a Chewie falcon with R2D2 crew has zero shields and 1 damage.
The player uses R2's ability to regain 1 shield, but rolls a hit which turns the damage card face up.
However Chewie's pilot ability does not apply as you have not been dealt a face up damage card - you were dealt a face down card, and another game effect flipped it after it had been dealt.
Is that right?