A) You are transcribing two people chatting at a restaurant about an upcoming election. A waiter comes up and takes their order. You DO NOT transcribe the dialogue between the two speakers and waiter because it is irrelevant to the main topic.
B) You are transcribing an interview where the interviewer is on the phone with an interviewee. At one point, the interviewer mutes the call and has a short conversation with someone in the room with him who does not speak at any other point in the file, and their conversation has nothing to do with the interview. You DO NOT transcribe this side conversation.