Irvine's axe was found on the ridge about 700 feet below where the 1999 M&I Expedition found the 1924 oxygen bottle, just below the First Step. General consensus is thatthe axe was not in the fall line with Mallory's body, depending on who you listen to, and when you listen to them.
Binary solution set, Irvine was separated from his axe on either the descent or the ascent. If on the descent, Irvine's body needs to be between the fall line below the axe and the 1924 camp 6 site. If on the ascent, Irvine's body is most likely in the same fall line as Mallory's. Could be anywhere, but that's the first place to look.
They dropped an O2 bottle just below the First Step. If they each carried two, the second bottles would have run dry above the Second Step, at today's rates of forward travel. I do not subscribe to Jochen Hemmleb's theory that M&I carried three bottles each. yes, his logic is impeccable, they might well have had that many to use, but the note his conclusion is based on does not prove, as he seems to believe, that they did take three, instead it offers substantive evidence that they took more than one each. "More than one" does not equal "three", and claims to that effect undermine scientific objectivity.
It's hard to give Conrad Anker's account of the Second Step's difficulty much credibility, solely because he changed his story. He said 5.8, no problem at first, then said 5.10, too hard for Mallory later. I prefer to give more weight to Conrad's belayer (Dave Hahn) on his climb since his story has remained constant. Hahn says Anker was up the crack before he could even set the belay.
With Mallory's goggles found neatly put away in his pocket, I prefer to believe they ascended the Second Step successfully and turned around at an indeterminate point above there, and that an accident occurred below the First Step during a night time descent.
With the first O2 bottle discarded below the First Step, the timing for a successful summit is tight. If Odell saw the pair ascending the Second Step at 12:50, they were approximately three hours off pace compared with Anker and Hahn. The summit pyramid has unstable snow conditions which can delay progress, and did, in the case of Hahn and Anker. My gut feeling is that M&I ran out of time and turned around, unsuccessful, somewhere above the Second Step, but given Mallory's fixation with the mountain, I do not rule out a successful summit, even after dark.
The Chinese expedition's confirmation of a second body on the steep part of the ridge between the First and Second Step's support this contention, as this is, generally in the fall line with Mallory's body. However, it raises significant questions as to the body discovered by them near high camp, notably that the position and confirmed presence of a sleeping bag do not match the conditions surrounding the discovery of Mallory's body.
If the Chinese account of the sleeping bag shrouded body do not refer to Mallory, then there was one body too many on the mountain in 1975, the one in the sleeping bag, Mallory, and the one on the ridge.
That's about all we can "know" for now. Given that E News interviewed the Chinese personally and that they have a team in place and ready to search at this time, we may find out more when and if another body (and/or camera) is discovered, if artifacts are found above the Second Step, or if they are found on the summit.
Until then, it's all just conjecture.