I got this program working to my desires

It works perfectly well for any dates before 1582 in the Gregorian Calendar.

In later development I am contemplating what to do before 1582.

My current idea is to base years off of the Julian Calendar in the way 1582 works in this calendar. And I will go with the Julian Calendar to Jan 1st 1 AD

From there I will then eliminate the month of Manu to have it simply be Capricorn and go like that for BC years

Alternatively if I find that proleptic Gregorian is the most common system for dates then I will have the month of Manu not exist before 11582, because if the year isn't preserved to primary sources anyways then there isn't a point in preserving the year to the Gregorian calendar

In the future I want to reform the Mannic calendar to merge the month of Manu into Capricorn. There will be a short year, and then the feast of Manu will be the New Year rather than the first day of the Month of Manu