When Roma is presenting the Glengarry Highlands brochure to Lingk at the restaurant, there is an instance when ice is heard clinking in a glass, as if one of the two is drinking or moving their glass. The next shot doesn't reveal somebody having moved or drank from a glass.
The neon sign on the restaurant across from the office has 4 or 5 of its letters on each line not operating. In the scene where Aaronow and Moss are in a car across from the restaurant, all of the letters on the sign are illuminated, as can be seen out the window of the car behind Moss. When they get out of the car, the letters are, again, not working.
When Levene enters and exits the Spannel house, the rain is pouring immediately outside the front door. But after he exits the camera pulls back to reveal he is on a large roofed porch. So the rain would actually be falling some distance from the door.
While Shelley is recounting to Roma the latter part of his close of his $82,000 Nyborg sale, the office door is wide open, no lights are on in the office, and clearly nobody is moving around in the office. Then Shelley calls to Williamson for more leads. When the camera angle changes, the office door is closed and Williamson has to open the door to come out into the room to answer that "the leads are coming."
After the police interview Alan Arkin puts on his coat and leaves the office. In subsequent scenes his coat can be seen draped over the back of the chair at his desk. The coat appears and disappears in Jack Lemmon and Kevin Spacey's confrontation over the office burglary.
When Ricky is trying to get more information from Williamson about the robbery, Williamson's room door is open and the detective is in the room, close to it. After a while Ricky and Williamson walk close the same door and not only it is closed but the detective is no longer there. After one small cut to Ricky, Williamson is about to enter his room, and the door is open again and the detective is standing there, this time outside of the room, blocking the door.
Although the play was set in Chicago and the movie in New York, references are made in the movie to places around or near Chicago. Levene refers to the meeting in Kenilworth which is a suburb of Chicago. Levene also mentions fishing for muskie in Wisconsin. Moss gets angry and says that he is "Going to Wisconsin." Characters in New York wouldn't reference such places.
As Blake points out the months First and Second prizes he mentions that First prize is a Cadillac, nodding towards the board over his right shoulder. He then asks if they 'wanna know what seconds prize is? A set of steak knives..' - when the steak knives can be clearly seen on the board below the Cadillac.