chaimboruch, that’s a ridiculous comparison.
Day 31 is not a major life-affecting halacha, very unlike the nidon didan. So, yes, Day 31 is not necessary to be up-front about when any chassan/kallah would learn about such shitos in their classes. But none of the (non-Gur, certainly) girls will learn about those of the nidon didan.
Mo is not relevant here.