In the story, we learn that Rob has been with the show for 10 years, and Buddy and Sally a year longer than that. And we know the show continued for at least three more years. This would make the Brady show an exceptionally long-running one; for example, the real-life "Carol Burnett Show" lasted 11 seasons; and "Your Show of Shows", for which Carl Reiner was a writer, only four.
Laura: "Darling, don't you want your beans and sauerkraut?"
Rob: "Don't bring those traitors into this bedroom!"