So having previously had his face smashed beyond recognition, one assumes there to have been copious blood loss, and as blood doesn't run upwards, his neck and pyjama jacket are the places most likely to have been soaked. I don't recall such being so.
If we look at what you suggest, IF he'd been moved from Aga to chair, he must have been alive because of the blood flow around/down the coal skuttle. Do you think they'd have left him to die like that? It's already been suggested that police shot June and Sheila.
It was the two bullets to the jaw that disfiguered Nevills face and caused bleeding, Jane!
But! the initial beating may have indeed been when Nevill received most of his other facial injuries, as well as the fractured skull.
Now here's the thing, when I had my nose broken it didn't bleed much at all apart from literally a few drops, nothing more, but it was knocked over to one side. And here's the funny thing, it almost set in that position right away! I went to the local hospital that night and the nurse took hold of it and it was set fast, so she said to go to my GP and see about it, but I never did, and the next day I had two black eyes!
Talking of bleeding, there was another time when I shot a nail through my finger with a nail gun, and again there was no blood loss! The nail went in at one side and out the other, sealing up each side instantaneously. I had to go to A&E with that one, and a doctor pulled it out with a pliers, only then did the finger bleed quite a bit.
Of course bullet wounds never seal themself, but I did read that its often better to leave a knife or other sharp object insitu for fear of further bleeding and damage removing it.
Anyway, the point is, from experience I believe that Nevill could have sustained quite serious head and facial injuries with minimal blood loss, so blood soaked pyjamas were not inevitable, Jane!
And yes, I believe that Nevill was alive while lying against the Aga with no bullet wounds at that time and got up again by himself before ending up on the chair/scuttle after being shot!