I'm not sure if this is the same guy, but a Sherpa bivouacked overnight at the summit with no oxygen, just to show it can be done. Well, this was word of mouth from a "Khumbhu doctor" (pro route-setter for the Khumbhu ice falls) when I was in the region years ago. The guy he was talking about had summited multiple times, and set all kinds of unofficial speed records for ascent + descent, but was kind of off the radar because he was on the worker side of the industry, not the sponsored climber side.