Near the end of the film, the Dangerous Woman approaches GK, Noir, and the Johnson Sisters sitting second-to-the-end booth of the diner. Dusty and Lefty are at the counter. They don't leave, but they disappear after the Dangerous Woman enters the diner.
When the Dangerous Lady enters the diner, her top left button is covered by the lapel. In the next shot, the coat is open more and the button is exposed. Then in the next shot, the button is covered again.
The cigarette behind Guy Noir's ear changes positions between shots.
The second time the chessboard is visible, Black's bishop takes White's rook in the near corner. The third time the chessboard is visible, the rook is back on the board.
In the Lobby scene, when Guy Noir talks to Donna, the make-up lady, he leaps over the bar to retrieve something. The bottles on the bar change just before he jumps over as the camera angle changes. They change again after he leaps over the bar.
While Guy Noir sits at his desk, an "On Air" sign, common to radio and TV stations, is lit. In a later scene, the show is still on the air, but the sign is switched off. It should be on whenever a microphone is open in the studio.
The group of four people sitting at the table in the diner react as if the Dangerous Woman is walking toward them (changing their facial expressions, changing their postures, moving their eyes, etc.). In the next shot she has not moved from her position just inside the doorway. She then begins walking toward them.
At the beginning of the film, Guy Noir leaves Mickey's Diner and walks to the Fitzgerald Theater where the program is performed. The theater is up the street and around the corner from the diner. He could not approach the theater from the Diner and see the big neon sign. From his angle he walked up a block, turned right, walked one more block (parallel to the theater), then turned back around to face it.
Lefty plays the guitar right-handed. This might have been an intentional subtle joke if Dusty had played left-handed.