Awesome explanations Alan, much appreciated!
One thing I noticed, while T400CN was on the market, its mask was barely orange at all, more like a pale tan. Its successors, BW400CN and Portra BW400 reverted to a deeper orange mask much like standard color negative film making them more difficult for standard darkroom printing. T400CN was somewhat closer to (but not completely like) XP2-Super in that regard.