Geo 49 dating
As different monarchs begin their reigns at different times, the exact month and day when a regnal year begins varies across reigns.
For example, Elizabeth I's regnal year starts on 17 November, James I's on 24 March, Charles I's on 27 March, and so on.
"30 January, 1648-49", the former being the legal year, the latter the historical year).
The regnal years listed below are given in normal historical date (not legal year).
So events before 1752 in English records often differ from European records, and it is sometimes necessary to refer to both sets of dates using "Old Style" (Julian) and "New Style" (Gregorian) notation, e.g.
the Occasional Conformity Act of 1711 is officially referenced as "10 Anne c.6" (read as "the sixth chapter of the statute of the parliamentary session that sat in the 10th year of the reign of Queen Anne"). When a monarch dies, abdicates or is deposed, the regnal year comes to an end (whether the full year has run its course or not).
In the event of a second session, or a second Parliament, in the same regnal year the chapter numbering would reset. A new regnal year begins from a new date, with a new monarch.
So a parliamentary statute that was passed on, say, 10 February 1585 (in normal calendar date) would be dated in the official record as 10 February 1584 (the legal year), and simultaneously said to have been passed in the 27th year of Elizabeth I (the regnal year that started on 17 November 1584).
The 1750 Act reforming the legal year also officially introduced to England the Gregorian calendar on Thursday 14 September 1752.