I have to tread back on this. They are marked as conflicts, BUT they are not registered as such, because no_update does not trigger an insert into the database.
Options are to change the status of the message_key to "kept_local" with all the DB changes this entails, or to convince the system out of the normal procedures to do so, to record a conflict.
I will look if I can manage to achieve recording of a conflict in the database that triggers the showing of the conflict screen without the need to change the data model.