Or in that case, demographically, I'd probably think of it as all the daves being one individual?

Like, on an abstract mathematical level, where you can kill someone such that more than one person is removed from the population, without there having been a previous "birth" even that correlates with each death, I can't quite get there.

I guess if you ran the deathrate-less-than-one scenario on rewind you'd get uncreated eternal people dying, but even that is more a birthrate less than 1 than a deathrate greater than 1.