Board Thread:Policies/@comment-13887191-20131206231713/@comment-220364-20131207233853

Earth-Prime was originally conceived of as the "Real World" in there were no super-heroes and people there could "tune in" on the other Earths for inspiration to write comic books. That sort of went out the window right after it was incorporated into the DC multiverse.

As far as the rest...
 * See Superman, Supergirl, Ultraman, and Power Girl for all of the variations of the characters and namesakes.
 * Superman Prime is a specific, deranged, version of Superman. Few, if any, of the later versions trace to that character. Rather they trace to New Earth, Earth-One, and Earth- Two versions.
 * As far as additional versions of Kara Zor-El... to be honest that amounts to fanwonk. DC never published anything with Earth-Three, Earth-Prime, or Earth 3 versions of the character. As a fan, without a specific in-story yes or no, you can speculate, but that's all it is - speculation.