Factual error: After the train crash, the teen characters discover cube-like items. One of them states it looks like a Rubik's Cube. The movie itself takes place in 1979, but the Rubik's Cube, although invented in 1974, was not licensed to sell in the USA until 1980. It was not even called a "Rubik's cube" until 1980 (prior to this, it was known as a "Magic Cube").
Factual error: The film opens during the winter, then 4 months later you see that school is out for the summer which should be June. When Joe is visiting Charles the TV is on and Walter Cronkite is saying "the potential is there for the ultimate risk of a meltdown at the Three Mile Island atomic power plant". The meltdown at Three Mile Island had already happened by this point.
Factual error: When Joe is in his room painting one of his monster models you can see in the background a model of the Invisible Man. This model was not released until 2009 by Moebius models. Although the model was created in the classic Aurora models style, this model was not available during 1979.
Factual error: The morning after the film's pivotal train wreck, Joe and Charlie are watching coverage of the story on local TV. The typeface on the screen is the now-ubiquitous Microsoft computer font "Arial", most recognizable by its distinctive 'R'. However Arial was not invented until 1982 and not in broad use until after 1990. The movie is set in 1979.
Other mistake: The Super 8 cameras used are both sound models, one Eumig and one Kodak, but when the film and film boxes are shown, they are the normal Super 8 silent cartridges, which are square. Sound movie cartridges are rectangular to accommodate the sound recording mechanism in a Super 8 Sound camera.
Factual error: In the scene where the Air Force Colonel is speaking with the Deputy Sheriff at the train crash site, there are two mistakes with the Deputy's uniform (in Ohio, all 88 Sheriff's Offices use identical uniforms). In the movie, the Deputy's badge is a 6-pointed star. In reality, it is a 5-pointed star. The "Deputy Sheriff" shoulder patches in the movie were adopted in 1997. This movie is set in 1979.
Factual error: When the kids broke into the school after being evacuated, the military bus used to transport them back out of town was too new. The front panels and grille on the bus show that it is a Blue Bird All American RE built between 1989 and 1999. The Blue Bird All American RE available in or before 1979 would have been mostly one panel on the front and had no grille. The bus in the movie was modified.it had headlights that resembled a Blue Bird from 1979, but even then the exact front light configuration was not accurate. It is plausible that the US Air Force could have specified a different headlight arrangement, but the front panelling of that bus would not have been seen until 1989 when the All American bus was given a face lift.
Continuity mistake: When the kids are gathered to film on the hill with the train crash in the background, Joe grabs the camera to get a closer look, setting up the tripod a couple feet away from Alice. Joe hunches forward to look through the camera. Then the group is shown from behind and Joe isn't hunched forward anymore. Alice is still a couple feet to the right and Cary a couple feet and forward to the right of her. When the camera comes back around to the front of them, Joe is hunched forward again, and Alice & Cary are right next to him.
Plot hole: Things have gone "missing" throughout the movie, without leaving extensive damage... I find that very strange. This is a HUGE alien that looks around for things he needs, carelessly flinging junk around in a junkyard, including a toilet, a motorcycle, and a stove which ends up landing out in the street. Izzy, the owner of the Auto Sales lot, shows the deputy that something is missing from the cars in his lot by lifting the hoods up. He doesn't say, and the camera doesn't show, WHAT exactly was missing from the cars, except the Bonneville. "Look at my Bonneville over here! They'd have to have a winch to take that out." This implies that it was only the Bonneville that had the engine removed, because you would need a winch to remove the engine from ANY of those vehicles. No other damage was visible. I don't see the huge alien being able to free the hood latch and lift out the engine without leaving other damage. Also, Debbie said there were 20 microwaves missing from her inventory - just "gone". I don't see the huge alien opening the door of a warehouse or store, walking through the doorway, and walking out with 20 microwaves. Even if he used a warehouse garage door. There would be other damage. It would have made sense if any business' missing items ended up looking the way Kelvin's Gas Station looked when the alien grabbed Sheriff Pruitt and Breen.
Continuity mistake: When the kids break into the school and discover the footage of Dr. Woodward and the other scientists, they break a window on the classroom door. The glass is almost completely removed from the frame but once the military arrive and take the kids away, there is suddenly more glass in the frame.