This can even occur within the crossover story itself: in "Judgement Day" Johnny Alpha travelled back in time from 2178 to 2114 to arrest a time-travelling criminal so he would not wipe out Earth (and thus, the future). The death of three billion people and destruction of five whole mega-cities then seemed to have no impact on Alpha's era. It was never explained in the story how an event as significant as a world war did not appear to be remembered by history in Alpha's era. On top of that, the future history of "Strontium Dog" bears little resemblance to "Dredd", with no mega-cities and mutants as an underclass in 'norm' cities in 2150. ("The Americans" in Judge Dredd Megazine no. 283 implied that "Strontium Dog's" nuclear war "will" occur in 2150, but this was a MacGuffin to drive the story forward.)