The word "canon" meant nothing to me back then. I did care about continuity.
Which is roughly how I came to it, through Doctor Who - the difference between continuity and canon came through finding out why some books said the Cybermen came from Mondas, and some from Telos, and how the Doctor had met Ian and Barbara (and Jo, come to that) in two different ways, and eventually learning that it was because the TV series was canon, and the novelisations sometimes changed it (because the previous story hadn't been done yet, and at the time they never expected it would be).
As a side note, an interesting example comes from the novelisations (one per season) of Howard's Way, a 1980s BBC Dallas-style drama starring Maurice 'Lytton' Colbourne about back-stabbing businessman in the yachting world (hence nicknamed 'Soap and Water').
The novelisation for season four (or about then), written like the earlier ones by the series's script editor, had to open with an introductory note along the lines of "You may recall that in the previous three books, I've mentioned that Charles Frere was an orphan and a self-made millionaire, and may therefore find the sudden appearance of his very rich father a bit puzzling. Well, that was what we assumed while we were writing the previous seasons, so I included it in the books, but we never mentioned it onscreen, and we've changed our mind, so live with it: it's what's on telly that counts".