One of the reason airliners are so safe is that every single part is tracked for its entire lifetime. There are a metric shitload (technical term) of serial numbers on an airliner identifying all the various parts. Once you have the serial number of a part, it's trivial to link that back to the airplane it was in, since it's all tracked.

For comparison, consider that debris from MH370 was positively linked to the airliner despite the fact that the plane disappeared almost without a trace and only a couple of pieces have washed up on shore: https://www.nytimes.com/2015/09/04/world/asia/malaysia-airli...