I think I've got more of that stuff, labelled as "Oxford 73 soundcheck", although in even worse quality (you call that very good???).
I would say that Freddie's comment "sounds like a wet fart through the monitors" is very strongly supportive of this being A soundcheck - if it was a studio, there would be headphones or speakers, monitors are specific to stages (in this context).
Any other views?
This IS the soundcheck of Oxford '73. It is available in almost VG+ quality. The one I had was one big track, more then 20 minutes, I believe. They played some very interesting things, like Ogre Battle without guitar.
There are some nice comments during that soundcheck, you mentioned already one, P_G.
I didn't download this file, but the comment of 'a wet fart' did ring a bell.
After all, very interesting and this is certainly NOT a studio-version (In my mind, they never recorded a studio version of this song, but hell, who knows?).