I suppose the question of what constitutes the “Arrowverse” is of some conceptual or semantic interest (especially amongst us fellow nerds
). But if “sharing” is an intrinsic aspect of a “shared universe,” it seems to me that extinct series - like
The Flash (1990) - can’t qualify, because no part of the current continuity can retroactively affect them. Whereas, within the “conventional” Arrowverse, knowledge of Earth-1 can actively inform an Earth-38 story (and vice-versa). So perhaps we need a different term for the accommodation of characters from past shows…?
As for
Black Lightning, a good case can be made that it’s
not part of the Arrowverse… yet. But if it is incorporated into the upcoming crossover, I guess it becomes so.
On a related note: if the various Earths are merged in “Crisis,” who gets to be POTUS? On Earth-38, it’s currently someone named Plastino. On Earth-1, it’s Susan Brayden (?). And is it Trump on BL Earth (therefore, our Earth?) because former POTUS Obama has been mentioned?