Pretty sure that the implication is that it would only be those having tons of sex all the time that would have a calendar specifically for tracking menstruation for pregnancy risks.
The more Harold has tried to either push her away, or pull himself away, the stronger her affection [and apparently, her abilities] has become.
Of course, he's done it with purpose. His main concern has always been that if she's engaged to him that it could remove her from eventually joining...
I get it being 7.5 because it's a volume extra, but it is also clearly established to be 6.5 in chronology...But she also then calls him 'Apothecary' which isn't established until chapter 7...