This is an interesting detail to learn about history. However, like the article mentions near the end, the Gregorian calendar was adopted at different times in different countries. The Anglican Church didn’t trust the Catholics, so Great Britain adopted the Gregorian calendar in 1752 ( https://en.wikipedia.org/wiki/Calendar_(New_Style)_Act_1750 ). And they did their best to hide the fact that they were adopting a Catholic invention: it’s the “New Style Calendar” and they came up with a different way to choose the same date for Easter.
1752 is late enough that Benjamin Franklin, George Washington, Thomas Jefferson and others were born before that change.
I think that’s the reason that programming languages tend to adopt the proleptic Gregorian calendar and leave it up to the programmer to figure out when the calendar was adopted in the countries they care about.
Except that countries apparently had to answer various questions when they adopted the Gregorian calendar, and they didn’t all chose the same answers. Ideally, we’d have something like tzdb but for calendar adoption. But I guess the need doesn’t come up all that often.
1752 is before the invention of timezones, but that adds another curiousity about "what date did X happen?". On the calendar of Country A it could've been October 31, 1752, and on the calendar of Country B it would've been October 21...
The British (including the American colonies) also did an arguably even more confusing calendar change in 1752, by switching the start of the new year from March 25 to January 1.
Does that really mean that the day after 24 March 1750 was 25 March 1751?
I think so.
Look at https://en.wikipedia.org/wiki/New_Year#Annunciation_Style :
“Despite the unification of the Scottish and English royal crowns with the accession of King James VI and I in 1603, and even the union of the kingdoms themselves in 1707, England continued to use Annunciation Style while Scotland used Modern Style. This led to the act being recorded at the time in England as 6 March 1706 (rather than 1707), because in England (unlike Scotland) it fell before the new year began (on 25 March).”
It apparently caused trouble for travelers (from the New Style Calendar Act https://en.wikisource.org/wiki/Calendar_(New_Style)_Act_1750 ):
“WHEREAS the legal Supputation of the Year of our Lord in that Part of Great Britain called England, according to which the Year beginneth on the 25th Day of March, hath been found by Experience to be attended with divers Inconveniencies, not only as it differs from the Usage of neighbouring Nations, but also from the legal Method of Computation in that Part of Great Britain called Scotlond, and from the common Usage throughout the whole Kingdom, and thereby frequent Mistakes are occasioned in the Dates of Deeds, and other Writings, and Disputes arise therefrom.”
Although, I think “common usage” in that statement implies that it was common to just do what other countries did, except when filling out legal documents.