It's a fuzzy line, though, because abstractions and pedagogy get better over time too, especially for long-standing systems which become increasingly well-under

It's a fuzzy line, though, because abstractions and pedagogy get better over time too, especially for long-standing systems which become increasingly well-understood over time. Basically, I'm saying that the world of 50 years ago is probably much more comprehensible to a highly skilled 2020 human than it was to someone actually living in it. It wouldn't be totally comprehensible to either, of course, but certainly the added context brings a lot of advantages.