@eris the revised common lectionary is on a 3 year cycle so to know what lectionary year youre in you can divide by 3 and take the remainder where 0 = A
@eris so dividing the year by 3 isnt uncommon when interacting with the book. idk what the specific number there is significant for though if anything.
pretty much the only other calculations the book involves are even/odd year for the daily office lectionary and date of easter.
also there are 3 rcl years so each year focuses on a different synoptic gospel with bits of john sprinkled in