Back in the day, a lot of prime time programming was within the same continuity.
For example, the Fonz was friends with Laverne and Shirley, and ran into Mork from Ork. Facts of Life was a Diff’rent Strokes spinoff. CBS was notorious for their shows being in the same universe, with M*A*S*H, and Trapper John, MD, and a bunch of their sitcom characters being bests.
PBS is getting into the act, with Benedict Cumberbatch locking wits with Murray-arty on Sesame Street.