Yeah, but how often are we talking about exactly specific dates without referring to specific historical texts?

The Magna Carta was sealed on June 15, 1215 for the Julian calendar. But if you want the actual anniversary, it was sealed on June 22, 1215 using the proleptic Gregorian calendar. Do you want to know the date people remember, ir the date of the true anniversary?

The coronation of Henry VIII is listed almost everywhere you look as June 24, 1509. Except that's also Julian. The date of the Gregorian calendar is July 4, 1509.

We don't remember the proleptic dates. We remember the dates that were then in use.

And if you say you're just always going to use the contemporary recorded date, that's fine. Until you get to dates like February 29, 1700. What do you put in your system then?