Continuities, Crossovers And Crises

After posting about J'onn J'onzz, I googled him. Amazing. It read like a more complicated version of a superheroes summary that I read shortly after the Crisis on Infinite Earths:

the original versions of the All-American and National Publications superheroes;
their Silver Age revivals;
the coexistence of earlier and later versions on parallel Earths;
the coexistence of other companies' superheroes on other Earths;
the existence of other kinds of characters, like anthropomorphic animals, on yet other Earths;
an Earth where no one has gained any superpowers;
an Earth where versions of DC and Marvel heroes exist;
the Crisis that destroyed most Earths and merged five, revising their histories;
a single DC Universe with new versions of all the characters.

Although each hero is a series character, his or her life and career become a single episode in an all-embracing narrative.