Is what you have the really crummy bootleg?
It’s a bootleg, but the sound is pretty good. I have no idea about the source.
Yes, you’re right there’s a massive gap in regards to his concert music. He basically did zero films between 1980 and 1989, only theatre, concert works etc. And only a small portion of it has been released. I think he really wants to release it, on Zarathustra or some other label, but he’s fallen so much off the radar these days, it’s difficult to get the money needed. At least that’s my guess.