The ‘Halloween’ Honest Trailer.

I think that they had the right idea, here.  Just hack away everything that wasn’t the first Halloween — ah, the first-first Halloween movie — and go on from there.  Continuity?  Heh.  Slasher movies, my friends: slasher movies.  Call it an ‘alternate timeline’ if you like, and go on from there.

Besides, I hear that the suddenly-only sequel is pretty good.  That makes it easier to get away with this sort of thing.