Other mistake: Michael stabs the teen boy who goes to get a beer for his girlfriend. In the closeup, even though the teen boy was stabbed pretty much straight through the heart clear through to the wall, there is no blood whatsoever dripping on the floor or down his pants. If you cut the major arteries to the heart, there would be great volumes of blood streaming down both the front and back of the teen. Even if he missed the heart there should be blood.
Other mistake: In 2000 a Limited Edition of Halloween was released with 12 extra minutes of footage, filmed during the making of Halloween II in 1981. In order to air Halloween on TV they needed to remove and add certain scenes. In the original 1978 version, Dr. Loomis tells Sheriff Bracket, "I watched him for fifteen years, sitting in a room, staring at a wall, not seeing the wall, looking past the wall, looking at this night, inhumanly patient." In the Extended version, you'll see Dr. Loomis visit Michael in his room, and he's staring out of a window. Not a wall. (00:11:31 - 00:12:38)