Just a quick little factoid for the day......
'Happy Days' is a multiversal show. It began life as a sketch on 'Love, American Style' where the major difference was in the casting of Howard Cunningham. Harold Gould had the role, but Mr. C was recast with Tom Bosley once it went to series.
So we can't count the pilot segment as being part of the show's presence in Earth Prime-Time. I think the TV dimension which houses prequels of more famous versions (such as the Art Carney adaptation of "The Incredible World Of Horace Ford") would be a better fit for it.
At the height of its popularity, 'Fonzie And The Happy Days Gang' found themselves translated into Tooners, the denizens of the Tooniverse. Again, this show cannot be considered blended into a shared history with the TV series.
And there would be a Skitlandia version as well, thanks to a sketch on Sonny & Cher's variety show and, by extension, the "Quentin Tarantino Welcome Back, Kotter" sketch on 'Saturday Night Live'. (Cast member Michael McKean reprised his role of Lennie from the 'Happy Days' spin-off 'Laverne & Shirley' with David Lander making a cameo appearance as Squiggy.)
From the 'Saturday Night Live' transcripts site:[ suddenly, Lenny and Squiggy from "Laverne & Shirley" enter the classroom, brandishing weapons of their own ]
Lenny: Alright, nobody move! If one of you walks to me, everybody dies!
Barbarino: Hey! Up your nose with a rubber hoses!
Squiggy: Yeah? Well, up your gizzard with a rubber lizard!
Lenny: That's good. Did you just make that up?
Squiggy: I made it up in the car..
(Other televisiologists probably do combine all of these together into one timeline narrative, and more power to them. But the Toobworld Dynamic is based more on the reality of the visual than on an idealistic concept.)
I suppose eventually certain members of the 'Happy Days' cast will find themselves as inductees into the Television Crossover Hall of Fame....