I do remember reading a lot of fanzines from the time that just treated TAS as being TOS reborn. Many of those episode guides included the 22 animated episodes as being part of the fabric. I believe people still believed that up until the late 1980s too, it was Gene Roddenberry who really threw a hand grenade at TAS about the time TNG started up.
Well, no; even years before that, there was disagreement in fandom about whether TAS counted (if you'll pardon the anachronism, since nobody called it "TAS" yet). Not too long ago, I found a debate in the letter column of an early-'80s Trek comic from DC (Vol. 1 #25, cover date April 1986) about whether TAS should be counted as "real" Trek or not. Editor Bob Greenberger said that he thought it should count, while the series' author Mike W. Barr preferred to ignore it. (Actually Mike wasn't writing the series anymore at that point, but there was some hope he might come back.)
Not to mention that a number of the early novelists didn't seem familiar with TAS, either because they hadn't watched it in first run or because it wasn't in reruns where they lived. For instance, Yesterday's Son
is supposed to be set two years after "All Our Yesterdays," but there's no reference to "Yesteryear" ever having occurred.
So while there was never any sense of TAS being officially
discredited until Roddenberry's '89 memo, there was certainly a lack of fan consensus about its status and worth prior to that.
But Gene was decanonizing a lot of things at that time. Wasn't it around then he actually employed somebody to be the arbiter of what was and was not official Star Trek? I think when it came to some things they tended to throw baby out with the bathwater.
Well, he had his assistant Richard Arnold vet the tie-ins, which is something that Paramount and CBS's licensing people have continued to do, though not as stringently as Arnold did. Of course none of the tie-ins have ever been canonical ("official" only means they're licensed and recognized by the corporation, not that they're treated as "real" events within the canon), but Arnold imposed tighter restrictions on what they were allowed to do.
As for what Roddenberry considered non-canonical late in his life, that included TAS, portions of several movies, and (according to Paula Block) even a number of TOS episodes -- probably mostly third-season episodes, or ones that he'd come to think of as too fanciful, or ones that didn't live up to his hopes or otherwise had second thoughts about. (Remember how in "Where Silence Has Lease," when the ship comes across a "hole in space" almost exactly like the zone of darkness in "The Immunity Syndrome," Data pointedly states that no Starfleet vessel has ever encountered anything remotely like it? I used to think that was a continuity error, but now I wonder if it was a deliberate attempt on Roddenberry's part to decanonize the space amoeba for being too silly.)
I also used to love the little continuity nods. Fanwank I know, but things like the allusion to "All Our Yesterdays" in "The Counter-Clock Incident" and so on. The intergration between TOS and TAS is pretty seamless most of the time.
It was the show that finally made Kor a recurring villain as he was always meant to be, albeit without Colicos, alas. Although I feel that sequels like "More Tribbles, More Troubles" and "Once Upon a Planet" were a bit derivative.