Earlier quoted context omitted.
Old stools broke as well, but the ones that broke don't exist any more. Only the really good ones remain.
Most of the really good ones have broken too: The ones that remain have been lucky.
1. germinate new oak trees from genetic material recovered from lucky stool (1-20 years, say) 2. tend to trees as they mature (40 years) 3. fell trees, craft new generation of stools. (~1 year) 4. use stools until only a handful of lucky stools survive (500+ years) 5. iterate
if all goes to plan, by year 2600 or so the third crop can be underway