Valid Range for Gregorian Calendar 4714 B.C. to 9999
A.D.
Although this function can handle dates all the way back
to 4714 B.C., such use may not be meaningful. The Gregorian
calendar was not instituted until October 15, 1582 (or
October 5, 1582 in the Julian calendar). Some countries did
not accept it until much later. For example, Britain
converted in 1752, The USSR in 1918 and Greece in 1923. Most
European countries used the Julian calendar prior to the
Gregorian.