Out of the three examples given, I'd be most interested in Gamma World - The Fall changed the world and made it weird, and in terms of how long ago it was, having it where it's so long ago to be a myth feels too old. By that point, we're less in the ruins, and pushed through the other side.
Granted, I know some of the questions the family get asked suggest how recent it was, such as this for the Merchants:
quote:
If the Fall was a sudden and terrifying event [x stats]
If the Fall was a protracted struggle against extinction [x stats]
If the Fall was so long ago that few can remember how it played out [x stats]