That’s interesting. This seems to be the same text I mentioned in the earlier thread, but from a different website.
However, a “correcting” statement in the later manual makes it clear that there is no direct relationship with your “measured dynamic range” - either because these are subjective values often taken from prints and we are now using the direct values from the raw black/white point module, or because of the switch to RGB space. And of course, due to the non-parallel shift of pure black/white you explained above.