How often do people need to refer to someone whose name they don't know?

Say someone works as a cashier, for example, or a teacher, etc., (people who deal with plenty of people every day), when they want/refer to someone, (usually when the person is not around) it would be the manager, the janitor, or a/the student, an/the English teacher, etc., correct? And then, once they find out their name, do they not start to refer to them with their names?