So the background is that I am working on some code to translate a Gregorian date to an Ancient Rome date. Upon Googling ancient roman dates I have the formula down pretty solid. However, I keep seeing different endings for months and special days (Kalends, Nones, Ides).
What is the correct set of rules for me to correctly determine the spelling of these days and months?
(ante diem|pridie) (lower case roman numeral?) (special day) (month) (year) (suffix [AD|AUC])
Just for an example, I've seen Kalends, Kalendas, Kalendis.. I've also seen Ianuarius, Ianuariis, etc.
I found this source: http://www.latin.org/datecalculator.php
Not sure if it is always correct...