Yes, I have followed these threads and seen these graphs. I think they are based on white light and the subtractive system.
I am wondering if there is a distinction to be made that the definition of grade in the subtractive system is what you get with the provided numbered filter, and with regard to those discontinuities, the filter is not, in fact, correct for that paper at that desired grade. There is, after all, a set of yellow/magenta settings (i.e. colour head) that will give a smooth curve, just not with preset filters
The blue green system however forces you to find your grade by using the settngs on the enlarger with respect to the paper you are using. Again a smooth curve can be created with the appropriate settings.
Bob describes solarization or muddiness in the shadows. Other discrepancies are seen at midtone. I am not sure the two observations are related.
I think Bob's observations need more investigation for an understanding of what he is describing.