You'd think the past would be already affected with how long the originals have been gone and that Bendis would address this...but I guess the past is in some kind of frozen state or Bendis is just writing whatever the hell he wants.
Maybe they're not the past versions of the original five in Marvel-616. Maybe they're actually the 1963 versions of the original five from an entirely different Earth, and Hank pulled them across the dimensions when he was trying to snag their younger selves from the past.
That way, Bendis gets to have his cake and eat it, too. He can do whatever he wants with these five characters and not worry about screwing anything up.