The premise is that we wanted a fun way to track Duncan's "strikes" each day; if he achieves a certain average over a minimum time period, he gets his new Ryzen, Windows 10 gaming PC.
It doesn't handle the correct number of days per month, or leap years, or anything like that-- it would take tens of thousands of lines to reproduce the entire equivalent of .Net's "System.DateTime" implementation. Our simpler approach meets our needs.