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.
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)
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: When Michael beats the kid in a park with a stick, the attack only lasts a minute yet the new blood on the kids face is dried up, presumably from earlier takes. The dry blood effect is seen in more scenes throughout the movie.