Character mistake: At Duke Boudreau's bar, the potential recruits for the sting are told, "Gondorff is setting up a con on the North side". Later in the film, Agent Polk tells Lt. Snyder, "Gondorff is running a con on the South side". The actual address for the betting hall is not given, but it is just down the alley from Klein's, which does have a South side address.
Character mistake: On finding Harman's dead body in their caravan, Charley says 'You called it, kid'. Great line, but Harman didn't call it. Charley, in fact, called it by giving his address to Jewell., who passes it on to Molly, who then goes to kill both Harman and Charley if he can.