Bear in mind that in the 80s and 90s it would have been recorded on film stock and mastered to VHS before being eventually digitized for VCD and then DVD as the tech emerged.
I would guess that much of the original film would have either decayed, been recorded over, thrown out or made it into the hands of some studio tech. Porn is generally considered pretty disposable and it would be a minor miracle if any pre-2000s (and realistically pre-2010s) material is even available for remastering. All this stuff took up actual shelf space and I'm sure studios wouldn't want to hold onto it all.
Like for music, it's amazing how many studio masters for classic rock albums just got tossed, lost or recorded over. Occasionally stuff just turns up in someone's private collection.
Best bet is probably AI remastering from original release format unfortunately.