Other mistake: In all the shots of ET wearing the white sheet the two eye holes are about a foot apart, so he could see out of the holes properly, but when Michael finds the white sheet ET had been wearing he lifts the material and we see that the two eye holes are only about two inches apart, which makes no sense. (It was Gertie's sheet that had eye holes so close together).
Other mistake: The movie starts in September 1961 and we are told that the talent show is in June. During the talent show there's a big banner saying 1961 when it should read 1962.
Other mistake: Rattner and DiMone are game planning about Rattner's date with Stacy (Leigh). DiMone tells Rattner that all he needs to do to score with Stacy is play songs from side 1 of "Led Zeppelin IV" (Zoso). You then hear the song "Kashmere", which is on the album "Physical Graffiti".
Suggested correction: Damone (not DiMone), told Rat that when they were making out to put on side 1 of Led Zeppelin IV. The fact that Rat is playing Kashmir from Physical Graffiti is just to show that Rat was unclear about Damone's instructions.
Not sure if Rat is unclear about Damone's instructions... he said he had 4 steps to making sure that getting a date with Stacy and keeping her around, and if all else fails, to play side one of LZ-IV... seems that Rat would (should) have asked if he was unclear then at that point considering Rat had a crush on her throughout the movie. I think that it's more of a musical inside joke if anyone was/is familiar with the Zep catalog realizing two things - one, the first four steps of Damone's plan didn't work being that his character was pretty shady and fake (off camera...because you don't see Rat implementing any of them) and two, that "he can't even get the music correct" due to his nervousness.
Other mistake: When Sid committed suicide, the coroner brought him out of the office...not his room.
Other mistake: Towards the end of the movie when Paul Kersey goes into the doctors' locker room to steal an ID tag, he checks several lockers to see if they will open. All the lockers that he tries are unfortunately locked. The problem is there are no locks on any of the lockers. (01:13:55)
Other mistake: Rupert almost got to the end of the cue cards when he flips too quickly the one saying "Alive", partially hidden behind another he is holding in his hand, showing the one saying "again" too early. So Jerry asks him to go back. And he does, only to bring then from behind "again." There is a small bit when De Niro is off-camera, but for this sequence to go as shown, he would have slipped to the bottom/the back of the pile the "again" card that was already at the top and then put in its place one of the two he had already in hand, the correct one, "alive." The fact that "again", that was at the top of the pile, is pulled from the bottom instead, makes no sense. (01:08:50)
Other mistake: When the thresher blows for the second time, Mr. Ages slides down it into a large chamber into a basket. When he falls into it, he is translucent for a second.