Initially I shot a few test photos from about 6 feet of my dog's muzzle, obliquely - focus and DOF was spot on to my eye - this with my Sigma 50mm and Nikkor 24-70. It's a good target because of the hair and fur patterns. So I was quite happy.
I have since repeated the same tests using Focal which I had done prior to service. Though not perfect (what test ever is, and what camera ever is!!), there is a noticeable improvement - take a look at the Focal report summary. What it shows to me is that the overall focus performance is pretty even across all the focus points - clearly the centre groupings have a slightly higher QOF as would be expected, but the variation left to right, top to bottom etc, is really quite small. So, that's the improvement I noticed. Though clearly, as has been repeated here by me and others, test conditions have a huge impact on results - lighting, distance to target, focal length etc., so the results should never be taken as gospel - but it seems to me that my D800 has headed in the right direction!
Only some prolonged actually shooting in field conditions will finally reveal if the AF system works as it should - or at least acceptlably for me.
So, that's basis for my remarks following the adjustment by Nikon, LA.