Speaking of actual change, while I was mulling this over, my mind went (as it sometimes does) to Night Court, actually! Because even though it's a type of classic sitcom, and sitcoms really depend on (and so often can get away with) the reset button, Night Court nevertheless included relationship evolution, especially with Dan and Harry.

Like, the tender, honest embrace we get after Dan comes back from the dead, we'd never have gotten that back in season 1. The show had let Dan and Harry have increasing emotional honesty and intimacy slowly over time--but more than that, the show let this increase actually change and deepen the characters & relationship. It remembered their past, all the layers of it. \o/