There's a table called "U.S. Occupations with at least one million workers (2006)". Every type of job there has existed since 1948. There are no new job categories created with over a million workers.
But that isn't too surprising. Seventy-five years ago, we had "factory worker", "foreman", and "manager". Compare that to any large company today and see the variety of jobs being done.
Jobs, and therefore people, have specialized more, that's all.
There's a table called "U.S. Occupations with at least one million workers (2006)". Every type of job there has existed since 1948. There are no new job categories created with over a million workers.