If my 7th Great Grandfather, Lawrence Gailshiott signed his will on 4 March 1743 and died around the first of June 1744 how could that be about 3 months later?
I promise you, this is not any kind of new math nor am I intoxicated! It really is three months later.
We must first understand a bit of history and the calendar because it all changed in 1752 for the American Colonies.
Prior to 1752, the colonies and most of the British Empire operated under the Julian Calendar which did not calculate the actual time the Earth takes to complete a single orbit around the Sun. [i] It did add a Leap Day every four years similar to the current Gregorian but in reality, it was adding too many days and getting the users off the true date. So in 1582, the concept of the Gregorian Calendar, which was named after Pope Gregory but designed by Luigi Lillio who was an astronomer of his day, was first proposed and many Catholic countries adopted it. [ii]
It was determined that about 10 days too many had been added since the calculated beginning of A.D. Anno Domini and these would be dropped when converting. The Julian Calendar, established by Julius Caesar in 708 B.C. [iii] The British Empire being protestant, did not make the change until 1752 by which time 13 days had to be shaved off. What this meant was that everyone went to bed on Wednesday, 2 September 1752, and woke up the next day on 14 September 1752. [iv]
But that still does not help the initial situation. The other change was moving New Year’s Day from 26 March to present-day, 1 January. Therefore, 4 March 1743 was actually in 1744 by current standards but the year did not change until 26 March. [v] You may also see the date written as 4 March 1743/44 or 1743/1744 because they all knew it was already a new year.
Now you know.