He's positive these are famous negatives

fascinating story!
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Jury is still out on this one... the two trees in the lede photo are dissimilar - 3 visible trunks in Adam's shot, 2 in Norsigian's - as are the shadows they cast on the respective ground. The aspect of the mountains in the background with relation to the foreground is quite different as well, as if a similar, but different focal length lens was used.

Having snapped a few big-format pix in my time, I can testify it's not easy to make different views of the same scene 'a few minutes apart': moving a tripod-mounted big-format camera even a few feet screws up everything - horizon, focus, tilt and shift. Getting those adjustment all in whack is time consuming - even (especially) for a photog on the level of Ansel Adams.