https://genealogy.stackexchange.com/questions/132/what-is-a-...
https://genealogy.stackexchange.com/questions/132/what-is-a-...
> Imagine – a person could have been married on April 26, 1710 and died on Feb 2, 1710.
(Because the new year began on March 25 prior to 1752)
I'm trying to describe this without antagonism, forgive me if I fall. But your question to me sounds just like saying, "at what temperature does water freeze?" and claiming there is no answer because Fahrenheit and Celsius both exist.
I feel like the article makes a similar mistake in claiming that certain dates did not exist. They are simply different calendars and the dates existed even if no one called them that date when they happened. It's like saying the 4th of July, 1776 BCE didn't exist - of course it did but nobody called it that at the time.