Absolutely. There is a brief moment while the successful response code at the end of DATA is being transmitted from receiver to sender during which both sides have responsibility for delivering.

Should an interruption happen during that time preventing the sender from receiving and processing the response code, then duplication can happen. And such duplication can be addressed by deduplication on the receiving side. I am not sure if there is any RFC specifying how to do such a deduplication, but the msgid is certainly an important field to take into account when doing deduplication.

That doesn’t answer the question of what time should really count if the exact time of attempted delivery has legal significance.