I like that! Honestly I'd take it one step further and speculate that there's a whole range of Earths that have slightly different versions of the same characters and events as Earths 66 and 76, to account for the similarities and contradictions between stories:
Earth-36
Green Hornet TV universe (where Batman is a fictional character)
Earth-52
Adventures of Superman TV show
Earth-62
New Adventures of Batman Filmation animated series
Earth-63
Dick Gautier as Batman, 1973 Equal Pay spot
Earth-66
Batman TV show/Film/animated films/Challenge of the Super Heroes
(Where Green Hornet exists and is identical to Earth-36, but a dramatized TV version of his criminal exploits was made, events of the series take place from 1966-1968.)
Earth-67
Batgirl pilot (different introduction of Batgirl)
Earth-68
Batman/Superman Hour/The Adventures of Batman, Superfriends, etc.
Earth-76
Wonder Woman TV series
Earth-166
Batman 66 and Wonder Woman 77 comics. (Continuation of the Batman and Wonder Woman TV shows, slightly different introduction of Two-Face, events of Batman take place in or before 1966, Wonder Woman, Superman, Batman and Green Hornet are the same as on Earths 76, 52, and 66.)
Earth-266
Return to the Batcave (where Batman is a fictional character)
Speculation aside, regarding the main timeline, I noticed that there are some continuity issues with the episodes as aired. Specifically Aunt Harriet encounters and is familiar with the Penguin in Batman 2x27, "The Penguin's Nest"/Batman 2x28, "The Bird's Last Jest", but in Batman 2x42, "Penguin is a Girl's Best Friend"/Batman 2x43, "Penguin Sets a Trend" she appears to meet him for the first time. (As noted, there's a similar issue with Green Hornet's appearance in Batman 2x07, "The Spell of Tut" vs. the crossover in Batman 2x51, "A Piece of the Action"
Batman 2x52, "Batman's Satisfaction".)
It's possible this is just a continuity error due to the huge number of scripts being written in a short amount of time, but it could also be that the episodes ended up being produced or aired out of story order. Since the episodes are pretty much self contained, it might be possible to move 2x42/43 to before 2x27/28 on the timeline to account for this.