I doubt at that era Sherpas had experience climbing with oxygen either.

Do you have a source for this? I have read quite a bit about climbing in the Himalayas and I have never heard of Sherpas climbing at high altitude in the 1920s.

I'm not sure about other mountains, but the Sherpas were against climbing Mount Everest because they considered it sacrilegious.

Everest would have been covered in tibetan Buddhist prayer flags if that were the case.