Other mistake: In the opening credits, Bob answers the phone. None of the buttons light up when the phone rings. On that style of phone, the light would indicate which line to answer. The phone is obviously a prop.
Continuity mistake: In the opening credits where Bob is on the 'el' platform, the train car he is sitting in is different from the one he enters in the scene before. The car he is shown entering is an older car with small windows and the car he is sitting in is a newer model with much larger windows.
Deliberate mistake: The circular desk where Carol sits should be rotated 180 degrees so she is facing the elevators. How many times have you gotten off an elevator in a fancy office building only to see the back of the receptionist's head?
Continuity mistake: In the earlier episodes, the number on Bob's office door is 715. In the later episodes, the number is 751.
Factual error: The apartment makes no sense.There are 3 steps down to the living room which you might have in a house but not in a high rise apartment building.The hallway shows a door for another apartment which would put most of its apartment out past the edge of the building.