The 1998 HALLOWEEN sequel HALLOWEEN: H20 was a little bit ahead of its time, as it was the first sequel in one of the popular slasher franchises to come out of the '70s and '80s to openly disregard the events of previous sequels. Sure, there was the anomaly of HALLOWEEN III earlier in the franchise, but that was entirely separate from the previous two films. H20 was a Michael Myers movie that kicked three previous Michael Myers movies out of its timeline, acting as if HALLOWEEN 4, 5, and 6 never happened and contradicting plot points. H20 has since been ignored itself, by both the 2007 HALLOWEEN remake and last year's HALLOWEEN, but it was a pioneer.
It wasn't always a sure thing that H20 was going to completely ignore previous sequels. At one point the events of 4 – 6 were acknowledged in a line of dialogue. A student at the school Laurie Strode (played by Jamie Lee Curtis and now going by the name Keri Tate) worked at was going to do a report on a book written about Michael Myers' various killing sprees, and would mention Laurie's daughter Jamie Lloyd, the ill-fated heroine of 4 and 5 who is dispatched early in part 6.
This is an excerpt from one draft of the script:
Ironically, Laurie survived that night, but was said to have died in a car accident years later… leaving behind her only daughter, Jamie. The book maintains there is truth to the rumor that Laurie Strode is actually alive and well and living under a new identity. Claiming that she gave up her daughter for adoption to protect the eight-year- old from her psychotic Uncle. Bad idea. Last Halloween, Jamie’s mutilated body was found in a barn just outside of Haddonfield.
That dialogue was even meant to be intercut with flashbacks to moments from the films Jamie Lloyd was in. After her daughter was mentioned, Laurie/Keri has to rush out of the classroom to go vomit.
HalloweenMovies.com contacted H20 editor Patrick Lussier to see if the scene referencing 4 – 6 was ever filmed. Lussier replied,
That’s an interesting scene, but never one that I read or encountered in the footage. As far as I know, there was never a scene like (above) that (was) shot. There was a big rewrite shortly before production where several things changed, including the (removal of the) whole character Charles S. Dutton had been hired to play (which included a death scene in the middle of the film) although the (scripted) scene as described was never shot, or if it was, it never came through editorial (which would be highly unlikely)."
It makes sense that the references were dropped before filming, because both Curtis and director Steve Miner wanted to ignore the HALLOWEEN films that Curtis wasn't in. H20 wouldn't have worked if it had acknowledged Jamie Lloyd's existence anyway, because there's no way to explain why Laurie would have left Jamie behind and taken her other child John (played by Josh Hartnett in H20) into hiding with her.