I see someone discusses about the Masters.
Before Blizzard decided to explain away everything and, subsequently, ruin everything, Old Gods were just “there”.
Nonsense like their power level, how many there were, where they came from, what was their “goal”, hell even if we really defeated them and not only their physical forms etc was left vague, although I don’t know anymore if that was intentional on Blizzard’s part or they just didn’t bother.
The first major update on their backstory, as Chronorabbit mentioned, was during WotLK, but even then it was vague and incomplete. Mentioned as “parasites” by a Titan facility is misleading at best, since in this instance, the Titans are anything but unbiased on the matter. Loken manipulating the archives in this case doesn’t really matter, as he replaced one instance of “biased” info with another.
Cataclysm didn’t really gave any more insight other than the fact that Deathwing was driven mad by them. N’zoth being the one to specifically drive him mad is a later retcon, I think.
I don’t remember if Y’shaarj getting obliterated by Aman’thul is something first mentioned in Mists, but if it is, it marks the first occasion of Blizzard starting to clearly explain stuff regarding the Titans and the Old Gods and their power levels between them, which were vague. In older incarnations of the lore, the Old Gods fluctuated between being weaker than Titans to being stronger than them, etc.
Then Legion completely killed everything with the complete nonsense that is the Cosmic Powers atrocity of a map and left the Old Gods as husks of ther former lore. BFA was, in retrospect, a mercy killing.