It was just pointed out to me in the other thread that the uncertainty in the provisional rank is apparently one-sided. 11.9 kyu is actually the lower bound of one deviation.
So I was wrong, in some sense there is a “hidden” true provisional rank at 6 kyu, but the graph displays it at 11.9 kyu artificially - as a prov player loses against a 1d, their true rank slightly lowers, and the deviation shortens, making their graphical rank increase.
My freaking God. That’s REALLY weird.