This was operator error, sorry for wasting your time. After a good night's rest, and in the light of day, when I repeat my test there is no mismatch. I'm pretty sure I had different rendering intents in my first test (perceptual vs. relative colormetric). The rendering intent is a sticky on both softproof and profile conversion and I was toggling, so I must have got them different.
I'm suffering a gradual increase in these kinds of senior moments. Are there any good drugs for that?
FWIW, I was softproofing because I received a Blurb book that was garbage. I've made about 10 Blurb books over several years and have been reasonably satisfied with the quality. But this last one was terrible. Washed out colors, low contrast. After supplying them with much evidence, they finally agreed to re-print at no charge. Now waiting for the reprint to arrive.