Thanks so much for being so patient with your full explanation. The result boils down to: for AF assist with the SB-600, use AF-S focus mode and single point AF-area mode. Drum the shutter release.
This also suggests that in continuous shutter release, the subject might move out of focus, becasue the focus locked at the hal-press leading to the (sequence of ) shots (if the subject does that in 1/6 second, or multiples of that), and the images will be out of focus. But that's the tradeoff (price) for using the SB-600 AF assist. Perhaps that's why Stan in St. Petersburg uses single frame shutter release for ballet. (But he says that professional dancers have very predictable trajectories, more so than amateurs, with which I am dealing.)
D-7000 behavior, SB-600 NOT mounted:
() Verifed: when in AF-S focus mode, allows only AF area modes S or Auto;
(b) (expected) when in AF-C focus mode, then AF-C becomes AF-S or AF-A. If it becomes AF-S, then we expect that only the single point AF area mode is active. But if SF-C becomes AF-A, then we would expect that the selected AF area mode (such a 9-pt) would apply Right?
(But if the SB-600 is mounted, we expect that AF-C focus mode would remain in AF-S focus mode, so there is no point in selecting AF-C, just select AF-S -- as you have said several times.)
I have not yet compared the situation with the SB-600 mounted. I'll do that shortly.
I have also found that using these minimal modes appear to make the camera focus faster. Less computing load.
I just reviewed the related material in Darell Young's book. Even he says that this subject is confusing. What he says is, of course, consistent with what you say, and I did not find that he documents the undocumented point to which you referred above (I checked for that days ago).