On the 1st of January 1600, Scotland began to number its years from 1st of January instead of 25th of March.
The 1st of January from that day was adopted as the start of the New Year during the reign of James VI King of Scots. This was the start of a move from the Julian Calendar to the Gregorian Calendar.
The change over meant that in the year 1599 there were only 9 months.
James VI proclaimed that Scotland should start the year on 1 January from 1600. Following the Union of the Crowns in 1603 he became James I of England but no such legal change took place south of the Border where the new year began on 25 March until 1752. As a result the same day in January, February or March (up to 24th) can be in different years. A system of double-dating was used in some legal documents, for example, 1 February 1699/1700 where 1699 refers to the year which began on 25 March 1699 and 1700 to the year which began on 1 January 1700.National Records of Scotland