The H.C-B example cliveh proposes actually underlines the difficulty faced by all users of viewfinder cameras. They never get to see the lens image upside down or otherwise. All they have is a peephole approximately delimiting a segment of the visible world. So the only opportunity for upside down formal picture evaluation may well be in the darkroom. I think I have researched nearly everything available on H.C-B but I can't find any suggestion he looked at his contact sheets upside down. Certainly his mark-ups of those sheets are right-way-up.