I'm not legitimately making up random Earths and labeling them official. Superman Returns was supposed to be a separate using the first two films as a springboard. Crisis... kinda tried to link it all.
I used Earth-78 to make a point, I'm not saying those films are actually in that universe.
Hell, if you like, do this:
Pre-Crisis
2006 - Superman Returns: Prequel
2006 - Superman Returns
2019 - Crisis on Infinite Earths
Post-Crisis
1977 - Superman: The Movie: Extended Cut
1979 - Superman II
1980 - Superman III
1984 - Supergirl: Director's Cut
1985 - Superman IV: The Quest for Peace
1989 - Superman '78
2020 - Crisis on Infinite Earths
Or, you know. The previous version with modern day setting of all the films.
Hell, could throw The Richard Donner Cut in pre-crisis even though it doesn't make much sense. You'd have to say Superman started a relationship with Lois, impregnated her... and then made her forget they did it somehow.It doesn't have any timeline references, too. I'm... not sure.
Pre-Crisis
1968 -
Superman Returns: Prequel #1
1997 -
Superman II: The Richard Donner Cut
2006 -
Superman Returns: Prequel #2-4
2006 -
Superman Returns
2019 - Crisis on Infinite Earths
Note: Alternate version of Superman: The Movie with alternate dialogue, time travel and modern setting occurs. The same can most likely be said for every film.
Post-Crisis
1977 -
Superman: The Movie: Extended Cut
1979 -
Superman II
1980 -
Superman III
1984 -
Supergirl: Director's Cut
1985 -
Superman IV: The Quest for Peace
1989 - Superman '78 #1-6
2020 - Crisis on Infinite Earths
Can't really think of any continuity errors doing that.
Edit: with more thought, I end up at the beginning:
1. Different Earths
2. Same Earth, different timeline
3. Same timeline, modern day retcon
No matter how I do it, something isn't right.
1. Can't be different Earths, they're confirmed the same despite the fact Superman Returns was meant to be seperate.
2. Calling them different timelines is speculatory and not suggested in any media.
3. Superman Returns is "confirmed" to take place after Superman IV per Marc Guggenheim, which doesn't make sense. The prop dates and technology don't match.
I'll keep it the same for now.
I'll also put Supergirl before Superman Returns because that "serveral trillion light-years" feat is way too absurd to be true if it takes him 5 years to go 21 light-years and back. I'm going to assume that the scientists made a really bad estimate or the guy on the radio was exaggerating to get a reaction.