standard year of 1800

Because I want to change the standard year for using to print the calendar since 1800 A.D.
If I enter a year after 2000 A.D., the program will print a normal purpose; but, if I enter a year between 1800 and 2000 A.D.,for example ,1994A.D. Sep., though the amount of space before first day is right, it has other trouble.