[James2001]

For example, I can't find any evidence that The Adventures of Ozzy and Harriet and Make Room For Daddy, the first 2 US sitcoms to hit the 10 year mark (the former ran for 14- still the longest running sitcom on US TV, the latter for 11)

That's no longer true in terms of number of seasons, as It's Always Sunny in Philadelphia is now at 15 seasons. And even then, you have to caveat that with "live-action" because The Simpsons, Family Guy, and American Dad all come above that.

Still true in terms of episodes though, in live action terms. Sunny doesn't have that many episodes each season, some seasons of Ozzie and Harriet had as many as 39 episodes.