In article , "Trenchrat" wrote:

It was not until The Dark Ages 1500's year after JC calendar that the
leap year was counted.

Not correct. Leap year has been used since the time of Julius Caesar. The
change in the 1500s was instituted to correct for drift in the Julian
calendar, which (by instituting leap year every four years) averaged 365.25
days per year. The actual value is 365.2422 days, and the Gregorian calendar
in current use averages 365.2425 days.