I second the idea: find those records early, keep track of them forever. Your med school wants them, different hospitals want them, away electives, residency, etc. In my experience, no, there's not a norm. Some schools want titers, some want shot dates, some want original records from childhood. This stuff can all get taken care of, just not quickly and maybe not cheaply.
Requirements can vary quite a bit between med schools & hospitals, and what your med school does might not be adequate for other programs moving forward. When I applied for away electives last year, each program had an immunization form to download, and the info requested varied quite a bit between programs. I took my stack of those forms into my school's occupational health office...at the same time all my classmates needed those forms...and then my school couldn't/wouldn't give shots or draw titers...and my insurance wouldn't pay...and shots you're expected to get as a kid aren't necessarily kept on hand in an adult doc office. That's during the 3rd year of med school. And now I'm doing it again for residency.
Of note, if you're over 40 you probably stood in a line for a polio shot in elementary school. Good luck finding those records. Get an IPV if you don't have them around. Gotta be the grownup in charge.
Best of luck to you.