Deliberate mistake: Ash's car breaks out into the courtyard and the whirling, windmill thing batters the Deadites aside. We see the carnage a couple of times filmed from different angles, one Deadite, planted, legs apart, gets battered twice and the guys who come in from the left and are quickly jerked off screen are shown again seconds later.
Deliberate mistake: Joey finds Channard's photo of Capt. Elliot Spencer in the closed art gallery but Kirsty stole that photo and gave it to Pinhead in the second film, where it was left on the floor of Hell. Also, all the sketches of the box were amongst the things from Channard's institute but those pictures and the other similar ones were from Dr. Channard's home collection. They were never kept at the institute.
Suggested correction: It was actually in a room in the institute. Not hell. Easy enough to retrieve it.