How was the Back to the Future trilogy filmed?
They did the first movie as a standalone project in 1985. When it was successful, they filmed the two sequels as another project in 1989. They held the third movie “in the can” until the next year. There were a couple of cast changes because they couldn’t get the actors back. Most notably, Crispin Glover wasn’t available, so they got somebody who looked like him and re-used footage from the first movie. They also re-cast Jennifer (the girlfriend) because the actress got sick, and they re-shot some scenes from the first movie with the new actress. Sources: http://www.imdb.
