frustrating that this is so hard to do:
LOL! It's actually impossible. I'm surprised two reconstructed calendars can be as close as a day or so. There is no calendar that started in ancient time and remained as a time keeping device to current times.
There's confusion in genealogy research from when the US in the 1700s went from Old Style to New Style dating. It's almost impossible to line up dates that happened over 2,300 years ago.
Just celebrate Epicurus's birthday around this weekend and be done with it. That's as "exact" as we're ever going to get.
Happy birthday, master-builder of human happiness!