[PTTG]

Yeah, that one's got some problems. The inspiration for the worldline was my observation that Earth's population currently grows at about 2% a year, and so any one person is about 2% likely to have a child, on average.

If you just want to take that idea as the seed and make it work, then have it so that there's just a 2% chance of a newborn clone of oneself each year -- with no formal destiny set for it.

If, on the other hand, you want to play with the idea of someone being duplicated as an adult, one option is to turn off aging at the same time you turn off regular reproduction.

Both have potential, to my mind.

As for Mel-1, I think it relies on a somewhat Watsonian interpretation of the films. They're humorous, but meaningfully accurate, retellings of real events. Perhaps fictionallized in much the same way that 1776 is.