A wreck is a wreck is a wreck UNLESS it was in one piece and obviously landed due to a mechanical malfunction. Most of them went splat, ergo there was no way to do even simple battlefield forensics to see what shot it down.
Most of the "verification" came from the tail or forward panel data (serials, block numbers BuAer numbers, etc.) or from lesser sources such as engine or equipment data plates. First come, first served.