Factual error: Federal institutions have strict rules for inmates or patients based on the reason for their incarceration, including substituting metal utensils with safer plastic ones. Despite being convicted of brutally killing his family, Myers is still trusted with a sharp metal fork - resulting in the nurse's death.
Plot hole: Laurie calls the police from 1987 Winchester drive, and gives them that address. Yet the police responding to the call go directly to 1960 Winchester drive - where Laurie has run to and is now hiding - even though it's on the other side of the street and several houses down. (01:31:30 - 01:33:40)
Continuity mistake: Laurie drops the items in the mail slot twice at the Myers' house. (00:58:30)
Other mistake: In the original ending, after Laurie is pulled out of the cop car, Loomis is able to reason with Michael to let her go. After he does, he is shot to death by the police. This was obviously changed, but when Loomis is reasoning with him in the final cut, you can still see the police standing behind him. (01:46:00)
Continuity mistake: Laurie's hair changes from curly to straight frequently in the Myers' house.
Continuity mistake: Near the film's end, Myers crushes Dr. Loomis' skull with blood protruding from several parts of his face. In the following shot of him being dragged into the house dead, his face and head are perfectly fine.
Factual error: When Laurie, Annie, and Lynda are walking home from school on Oct 31st, you see the "fall" leaves on the ground, however the surrounding trees are as green as can be. (01:04:15 - 01:05:30)
Factual error: There's no way a body can be pinned to the wall with the tip of a butcher's knife.
Continuity mistake: When Laurie stops at the Myers house she has no backpack. She does in the next scene.
Continuity mistake: When Grizzly the truck driver stops at the truck stop, the attendant opens the hood and gets the hose twice.