Yes, your next stop was Postman Higher Grade, provided you could pass the test/exam. Done away with in the 2000 agreement. In my personal opinion I think that was much more destructive than equalising in the long run, especially since it lingers on as a synonym for the locker where all the extra responsibilities still exist but without the extra pay to make it worth the hassle.
Operational grades (as of the 90s?) ran something like:
Cadet > postman/woman > temp PHG > PHG > Temp JV(?) > JV(?)