Another mistake

In the syndicated episode just repeated, Jerry's girlfriend (the one who works on the sex/phone line) is near the front door when the buzzer sounds. She asks Jerry what to do (he's not in the room); he says something like "just press it / see who it is" - she clearly presses one button, Elaine identifies herself, she (girlfriend) says OK, come up, without pressing the other button. No buzzing in??