This thread was inspired by a completely random memory I had this morning. I first got into Star Trek when I was thirteen years old, in 1998. That year I borrowed the first six Star Trek movies from the library, one after the other, and when my uncle (who was an old school fan) heard I was getting into it he sent me a VHS tape he had put together full of what were, in his mind, the best episodes of the original series.
I knew about The Next Generation and the other spin-offs. It was the '90s, you couldn't not (I had gotten an issue of Disney Adventures Magazine in, I think, '93 that was all about the show). Insurrection wasn't out yet, First Contact was still a big deal (at least to me) as it was being hyped on VHS and DVD in rental stores.
Here's where the weird assumption comes in: Until I finally got around to watching the thing, based solely on the commercials for the home video releases, I thought for sure that First Contact was a remake of the Borg episodes of The Next Generation (which I had not seen yet, I had only read and heard about them). I could not tell you why I thought this, what previous media consumption led me down this thought path, only that, in 1998, I would have been adamant that was the case.
I am pretty sure I saw Insurrection in a movie theater in late '98 or early '99, and I don't remember if I rented First Contact before or after that, but I wasn't walking around with this assumption for too terribly long in the grand scheme of things.
Still... Weird.
Anyway! Did you ever make any weird assumptions like this about Star Trek? Maybe your youthful brain was working overtime, or you just misheard a line that didn't get clarified for you until reading a book or watching with captions on...