Maybe I'm spoiled by XKCD what-if, but that result doesn't tell me which of those people in 1980 are the same as in 1950, or new people. Or figure out how many

Maybe I'm spoiled by XKCD what-if, but that result doesn't tell me which of those people in 1980 are the same as in 1950, or new people. Or figure out how many people died young in between. If someone goes there for six months, is that living?