I’m pretty sure the TZ database takes this from the transition for English-speaking countries: https://en.m.wikipedia.org/wiki/Adoption_of_the_Gregorian_calend

I’m pretty sure the TZ database takes this from the transition for English-speaking countries: https://en.m.wikipedia.org/wiki/Adoption_of_the_Gregorian_calendar#Great_Britain_and_its_colonies https://en.m.wikipedia.org/wiki/Adoption_of_the_Gregorian_ca...