Is it possible to have two transmitters using the exact same header field, and if not, why?

When responding to a closed-ended question, only provide the information the interviewer has asked for. Since the interviewer is likely to follow up with an open-ended question to collect more information, embellishing your original response assumes you already have an idea about the follow-up question and are pre-empting the interviewer. You may also guess wrong about the follow-up, which will be awkward when the interviewer asks the question they prepared.

"No, it is not possible to have two transmitters using the exact same header field. Doing this would produce a conflict on the bus. This situation is typically addressed with middleware that ensures only one node with the same header can transmit at a time."