I remember trying to figure out 63 revisions years ago and getting a headache.
I kinda look at it this way, since all model 63's have recessed cylinders the deletion of the barrel set pin was not a change of any part.
In other words the parts on a non pinned 63 from 1984 will all interchange with a model 63 from 1978 so there was no reason to make a revision change.