I would think that a crack in a piece of glass is as distinct as a fingerprint... We seem to have a pretty good picture (if legit) of the windshield crack from 1963... and allegedly we have the actual windshield that was removed from the limo in the National Archives. A good closeup HD image of the windshield in the National Archives would allow a good enough comparison that would, perhaps, help us determine if the two windshield images are from the very same windshield. What I have seen so far says they are very possibly not from the same windshield....