In the scene where Dr. Johnson first meets Charlie on the street, the cars behind Charlie vary from shot to shot. In some there is a big white truck to the left and a car with flashing lights on the left. In other shots, there are only a couple of dark cars parked there
Just before Alan and Charlie go for a coffee, he has his headphone around his neck, few secs later when Charlie goes inside, he's listening to hes headphone.
When he walks up to the bar there on, split sec later there of again.
When Charlie is in his first apartment playing the video game and the shot is from where the video screen is, the receiver/amplifier has no cables or wires running to or from it; yet when he's in the second apartment, all the RCA cables and other cables are plugged into it and it is clearly hooked up to work.