It all depends on the country observing the calendars as not all countries changed from the Julian Calendar to the Gregorian in the same year. In England, in the Julian Calendar the first day of the year was Lady Day (March 25th), but I don't know whether or not it was the same for all countries. Under the OS calendar for England, March 25, 1676 was the first day of 1676 and March 24, 1676 was the last day. 3/24/1676 O.S. in England might be 3/24/1677 N.S. in another country. A you indicated above, sometimes the first day of the year in the Julian Calendar was the first day of Spring.