If you are working with the Historical data, you have to take into account when the country(whose historical data you are dealing with) adopted the Gregorian calendar. Most of Europe adopted from 1582 but UK and USA adopted it from 1752. Before that, I think it is Julian Calendar, but you might have to do some R & D.
All the date formats in SAS refers to Gregorian Calendar.
This is my understanding of Dates and Calendar. If it is not please let me know.