I'm trying to write down some of my friends' Hebrew birthdates, and because there's a bunch of them, I'm doing it in short. So 8 Tishrei 5763 would convert to 1/8/63 or ח׳ א׳ תשס״ג. (I think; I'm not entirely sure.) My question is how does this interact with the two Adars? So in a normal year, my friend who is born on Purim would be born on 6/14/62, but in a leap year, would that shift to 7/14? Or would the days stack so that it's written as 6/44? Or is there some other rule I don't know about? Thanks so much!!
(Note: here I'm using civil as opposed to religious dates, so Rosh haShanah would be on 1/1 instead of 7/1.)