Dr Johnson's Birthday - or is it?

Today is the birthday of Dr Samuel Johnson who was born on 7th September 1709 and died on 13th December 1784. He was one of England’s best known literary figures. A poet, essayist, biographer, lexicographer, critic, wit and prose stylist, he is the most quoted of English writers after Shakespeare.

So, if he was born on 7th September, how come the 18th September is his birthday? The answer lies in the change from the Julian calendar to the Gregorian calendar which took place in 1752 when we ‘lost’ eleven days to catch up to most of Continental Europe. After that change Dr Johnson celebrated his birthday on 18th September (New Style) which was 7th September (Old Style).

It is fairly widely known that in September 1752, Great Britain switched from the Julian Calendar to the Gregorian Calendar. In order to achieve the change, 11 days were 'omitted' from the calendar - i.e. the day after 2 September 1752 was 14 September 1752. This change was as a result of an Act of Parliament - the Calendar Act of 1751 An Act for Regulating the Commencement of the Year; and for Correcting the Calendar now in Use.
What isn't so widely known is a second change which the Act introduced - as named in the first part of the Act's title. The Act changed the first day of the year (or, if you want to impress your friends with a new word, the Supputation of the Year).
Prior to 1752 in England, the year began on 25 March (Lady Day). Lady Day is one of the Quarter Days, which are still used in legal circles. The Quarter Days divide the year in quarters (hence the name, and the Quarter Days are: Lady Day (25 March), Midsummers Day (24 June), Michaelmas Day (29 September), and Christmas Day (25 December).
So, in England prior to the Act, the day after 24 March 1642 was 25 March 1643. The Act changed this, so that the day after 31 December 1751 was 1 January 1752. As a consequence, 1751 was a short year - it ran only from 25 March to 31 December.
To throw some more confusion on the issue, Scotland had changed the first day of the year to 1 January in 1600 (in 1600, Scotland was a separate kingdom). When King James VI of Scotland became also King James I of England in 1603, the possibilities of date confusion must have been considerable.
Historians have to be on their toes with all dates prior to 1752. For example, in The Tower of London there is some graffiti scratched into a cell wall by someone imprisoned in January 1642 for his role in the Battle of Edgehill (which took place on 23 October 1642).