Well my last 2 data points with checked bags:

LHR-DBX in F, no tags put on at all and bags off within first 30 bags. ( only 3 F pax)

DXB-LHR n F, orange and F tag put on and bag came out 1 hour after first bag once all other bags had gone.....

So for me BA Priority bags are crap and at LHR a joke!