Looking for a list of alternate calendar codes

I was helping a client yesterday whose calendar dates were showing up with weird years, and I tracked down that his > Language and Region > Calendar setting was set to Japanese. (It showed the date with R5 instead of a year, so July 12, 2023 showed as 7/12/R5.) We fixed it by resetting it to Gregorian.

I noticed in the settings that there were a long list of alternative calendars available:

My question is this: if Japanese is listed as R5 (which appears to stand for Reiwa 5), are there similar codes for each of the other calendars, and if so, where can I find a list of the codes?

If not, how would the dates show up in settings for each of these calendars?

I get a lot of clients from other countries and would like to be prepared for the possibility of discovering other calendar types on their devices.

Zane