Apparently it was coined by Alger Hiss, but I've seen Jason Kottke use the term "The Great Span" to describe this phenomenon of a small number of generations spanning surprisingly long periods of time.
Looking at that tag on kottke.org, the top few results are a Civil War widow dying in 2020, John Tyler (president in 1841) having a living grandson, and a 2020 interview with the son of a formerly enslaved person. Wild stuff.