What's funny is, based on what was seen on the TV in HIII, the Myers Halloween is fictional and the HIII world is the real one.
Unless they want to go full meta and say that movie we saw was a fictional account of an actual event, and they both take place in the same universe, and they explain other sequels didn't get made due to the citizens of Haddonfield and Laurie complained of the movie's insensitivity of trying to capitalize on a tragic event, taking a jab at Hollywood and the popularity of slasher movies in the 80s.