Each campaign is meant for a different Power Level. Usually villains are built on a single Power Level and stay there, in which case each adventure would be experienced by a different group of villains who exist in the same world. The results of the campaign can carry over to the next, but usually not the “heroes.” It’s usual but possible for a villain to start at Power Level II in Necessary Evil: Breakout (chronologically the first story), experience an unusual event that bumps them up to Power Level III for Necessary Evil: Invasion, and then in the intervening decade somehow that villain ascends to Power Level V in time for Cosmic Crisis.
That’s not the standard way to do it, but it is a possibility!