Novelizations and published versions of the script used to be so much more important in the days before we could own movies in our own collections.
My point was, people might still have found those things annoying at the time, but the studios themselves
weren't quite as fussy about whether continuity matched exactly from sequel to sequel. I'd expect them to care about it a great deal more now, because they'd know that we're all going to be rewatching the movies multiple times (and, often, in close proximity to each other - no two or three year gaps between release dates).
Though to be completely fair on Back To The Future
in particular, Zemeckis, Gale and co did an absolutely astounding job of matching up all those 1955 scenes with the ones we'd seen in the first movie. On the whole their continuity was spot on, possibly a stand out compared to most movie sequels (home video was very much a factor by 1989, of course).