I can tell you from my experience that I was purchasing model 29-2s in the late 70s and they had gone to a bluing process where the frames were one shade of blue and the barrels and cylinders were another.
I also saw a few that came through from the factory that had "push off".
The 29-3s were ok with the bluing but the fit and polishing was less than the model 29-2s.
I think that a general way of looking at it is that as time went on, the quality fell due to production costs.