It's hard to figure out unless they had persistent memory elsewhere.
The reason they could tell that a message was deleted is because the existence of a "message deleted" message is itself a message telling them they are be moderated. The lack of this message may make it impossible to determine if this is the first attempt at comms or the 1000th.
The reason they could tell that a message was deleted is because the existence of a "message deleted" message is itself a message telling them they are be moderated. The lack of this message may make it impossible to determine if this is the first attempt at comms or the 1000th.