That's from James Brundage's Law Sex and Christian Society in Medieval Europe. It is not about when/whether people actually had sex. It is about the constraints that Medieval Cannon Law put on Sex. Brundage is the leading scholar on that subject, and as far as I know, his book and chart are accurate.

It's from "Law, Sex, and Christian Society in Medieval Europe" by James A. Brundage. It's a generally respectable work, with proper citations and everything. These things really are mentioned in penitentials. So it's definitely accurate.

The big question is not about accuracy, though. The big question is what is the consequence of something being declared sinful in a penitential.