Optically, I don't think there are any differences between any of the Macro lenses going way back. I even think the new AF version follows the same design and probably why you see no differences in your test.
The only changes between the D and non D is the lens coatings used. I have been told this reduces chromatic aberrations when focused up close but have never seen any tests to conform this.
I own the Phase 120D and its a stunning lens but like me if I upgraded to the AF version apart from the obvious inclusion of AF the optical performance is reported to be just the same.
This was also my conclusion when I compared the 120mm Af and 120mm AF "D" lenses. The results - from center to corners - were practically identical. I did not encounter chromatic aberration, but I have seen that illustrated on some other legacy Mamiya glass when compared to "D" version Phase One/Mamiya lenses. In particular, the 80mm/2.8 AF exhibits more chromatic aberration wide open than the 80mm/2.8 AF "D" version. My assumption is that the "D" version of the 120mm will produce a similar reduction. The below link is a good illustration of how "color pollution" is reduced from the legacy 80mm AF, 80mm D, and Schneider 80mm LS. If you scroll down to the 2nd lens test that shows "Pr" text, you're there.
Lens :: Capture Integration – Medium Format Digital Back Sales & Rental and Other Professional Photographic Equipment
The Mamiya 120mm Macro has been, and continues to be an outstandingly sharp lens. The amount of resolution improvement on the legacy Mamiya lenses is limited to what is possible. And some lenses simply left very little or no room for the physical possibility of increasing the resolution, as they were already extremely high resolving lenses. Thus, the coatings are sometimes the primary difference, with the result being fewer occurrences of chromatic aberration.
We recently tested the 120mm D with the 120mm AF, and found the AF, if anything to be just as sharp, perhaps even - if so, just by a hair - a bit sharper. Raws are not downloadable from here (PM me for those if you like), but the parameters and conclusions of the testing process are:
Phase One 120mm AF vs. 120mm MF :: Capture Integration – Medium Format Digital Back Sales & Rental and Other Professional Photographic Equipment
Steve Hendrix