In my experience, if the check-in staff is non-bmi (i.e. Aviance), they sometimes forget to tag the bags. Often they do not bother if the plane is an Embraer jungle jet.

Out of my last 5 flights were the bags were properly tagged, I got them prioritised in 4 occasions. The fifth one was pointless as the carrousel was used for BA flight at the same time and it took ages.

In my opinion, you are wasting yours and everyone else's time but good luck.