I can't know for certain, but I think it was not *just* the fact that previous calibrated bodies were +10.
The reason I say this is that the first repair attempt shifted the whole thing +15 to +20 (on center points) which made the previously unreliable left hand sensors OK, but threw the previously reliable center points way off.
More succinctly, the first attempt to fix did not address the focus differences across the frame (for me). IMO it did prove that the outer AF sensors are indeed capable of rock solid focus (which, really we already knew because the right hand sensors worked pretty well to begin with).
The first attempt did slightly improve the difference in reliability between the left and center sensors. However, it did not totally solve it, and in some ways made it worse because 4 out of the 5 lenses I owned now required AF fine tune values of +10 or greater (2 of which were +20) for the center sensor. The only lens that didn't need it was my copy of the AF-S 70-300 VR f/4.5-5.6 which probably masks the issue due to it's increased DoF.
The jury is still out on the second attempt as I haven't received mine back from service yet.