Our member numbers in SAI are our chapter number followed by a dash, and then the number they have us listed in the chapter roll, which within each class is done alphabetically, but each class picks up after the last one, of course. I didn't actually know what my member number was until I got my first Alumnae Association card, and it was on the letter above my address.
Sounds like we do it much like AOPi and DG do, actually. Exception being that where
titchou said DG has it as "001" ours would just be "1" lol.