Off topic but I watched that Back In Time documentary and the "To Be Continued..." wasn't in the film's theatrical release. They didn't know there'd be a sequel, but wanted to end the film on them going off onto another adventure. They added that graphic for the VHS release, so everyone always assumed the sequels were always planned, because that's the version people remember. They took away the "To Be Continued" for the recent reissue.
They also said they wouldn't have included Jennifer in the final scene if they knew there were going to be sequels because they didn't know what to do with her after that.
Which is clearly why she's knocked out for the whole part 2 and part 3