Sometimes I really miss the days before the internet. Most of us probably wouldn't even know that a new Trek movie was being made at all.
Unless you were a member of a ST club that had a reliable, regular newsletter, "Starlog" magazine and TV's "Entertainment Tonight" (which was distributed overseas as a compressed "Entertainment This Week"), were often the only sources of hot gossip. Actual spoilers were even rarer, if you were lucky enough to know someone who went on a Paramount Pictures soundstage tour during production.
Transwarp Drive wrote:
Gene leaked like crazy when TOS films were around back in the day.
Well, he did get Susan Sackett to leak Bennett and Meyer's intention to kill off Spock, but that turned out to move the death scene to the film's climax instead of near the beginning, which Bennett eventually agreed made for a superior film.
The very first photos of ST II characters in costume were released in a Japanese magazine, "Super-Visual", in January 1982, and the film had its US premiere in early June.