I don't know the answer, but there's a famous lost camera owned by a team that perished on Everest before Hillary/Norgay successfully climbed it. It's possible that the camera contains proof of an earlier first ascent: https://en.wikipedia.org/wiki/George_Mallory#Reaching_the_su...
Kodak has published instructions for how to protect the camera and develop the film, if it's ever found: https://web.archive.org/web/20130303001517/http://www.veloci...