Food fortification is voluntary, not mandated, according to the link I provided. Thus the perpetual dead-end on the search for a "mandate". Amazing how one word can hang up a search(for a long time, for me).
The mystery that still remains, for me, is why iodate dough conditioners were used at all(in the 1960s) when the practice of using bromate was widely established. I have my theory on that, but it's just a theory.