This post is not going where you think it is going…
This is something I mentioned before, but I keep running into dating issues. Not just that most books and paintings of the 15th century are not dated but when dates are used, they do not correspond 1 on 1 with the dates we use now.
First of all there is the Julian-Gregorian conversion, which differs from region to region, and started from 1582. Due to timing issues caused by the method of the Julian calendar, it was decided to skip a number of days at a given time. The difference was 10 days at first, but it increments so now we’re apparently 13 days ahead. The result is that not only is it not clear if authors writing after 1582 are using the new date format or the old one when mentioning dates from a time before that, but you also have to factor in the incrementation between the author’s time and the current time.
The second issue is that the year in the middle ages didn’t start on 1 January but on another selected day, usually the day of an important catholic event such as the Annunciation or Easter. This means there is also some discrepancy in year numbers between now and eg. dates in the contemporary chronicles. To give a relevant example, it can happen that you find 1476 as the year when Charles the Bold died, instead of 1477.
I am not even going to mention the weird French Republican calender that was used during a few years around 1800.
It’s convenient we’re in lockdown and I have no idea of what day, month and year it is anyway.