Change number 1. The first of the overlapping generations could of been born in 1914. Didn't have to be 20 yrs old.
Change number 2. The second of the overlapping generations could be born when the first generation is 80
change number 3. 607 was wrong. Move it up to 587/1934. That adds another 20 years.
With these basic changes that the r&f will joyfully accept as new light the end could be 180 years from 1914. That's way longer than any of us will be alive. No plan b required.