I highly doubt he will cover every demo release made in the 80's
Guess that only from Africa, Caribbean Countries, Middle East, ex Soviet countries there are dozens and dozens and dozens of demos released whose information are totally impossible to find. Bands don't reply, bands don't share information, bands have lost all those tapes and recordings, it's also impossible to find even a shitty image of the tape cover nor even a basic tracklist....
Then I guess this situation is common also to the most "reachable" european or american countries....just in my hometown (Prato) there were 3 metal bands (Truth Zone and two more, one of them sung "Zona selvaggia") who recorded their own demo back in the late 80's (1988-1989) but I couldn't be able to find even a shit of information in more than 20 years....and Truth Zone's guitarist was studying in my same school and he always refused to talk about that demo (which I had in double copy at the time...)
Massacrator (pre-Necromass) released a Demo in 1989 and a live tape...I know the ex members and in 15+ years they never sent me a rip or a scan of the cover, despite hundred of promises...in fact if you see on M.A. it's still listed in the release notes and a tracklist is not available. There are 2-3 people I know in Florence who has that demo but nobody ever cared to share even a basic information
Plus, in 1990 I recorded a rehearsal tape with my brother and the guitar player of Dream Void, at the Casa del Popolo di Legri....we spreaded that tape in 2-3 copies and then it went lost (I overdubbed it a few time later, as it was a very shitty performance) and the other 2 copies are just vanished in the air. I don't even remember the name of our band....Desecration or Buried Alive (maybe we changed name at the second rehearsal for no particular reason). So, as you can see...there could be thousand of demos whose existence is known only to 2-3 people, if they are even still alive
From Spain I know 50 + bands (at least) who released demos in the 80's which are totally ignored by Metal Archives....and my friends overthere have dozens and dozens more obscure bands which I am not even aware of.
In India - as I posted some list somewhere - there were A LOT of bands in the 80's...and it's far beyond impossible to track down their history and even more impossible to know if they ever recorded something as most of bands from Asia and Africa do not even consider demo recordings as part of their discography or biography...there could have been a lot of demos circulating only in few towns which are completely neglected and forgotten, by the bands themselves first of all.
So...yeah....I think it's something beyond impossible as a target