Americans are cautious to confirm
http://mobile.nytimes.com/2015/08/06/world/asia/mh370-wing-reunion.html?referrer=
"...experts from Boeing and the National Transportation Safety Board were not yet fully satisfied that the part had indeed come from Flight 370, and called for further analysis before reaching a definite conclusion.
(...)
The person involved in the investigation said that no serial or other unique identifying number was found on the wing flap, making the job of identifying it more complicated. The person also said that so far, no burn marks or other evidence of physical damage had been found that might provide any further clues about the circumstances under which the plane went down."
So, no numbers...
Is there any chance of it being from some other 777?