Read it again. There’s not a “per when” because it’s measuring the Diasporas, which would just be “per all time, that are still alive”
Diaspora just means dispersed people. It doesn’t convey any time frame in and of itself
Yes, exactly, hence “per all time, that are still alive” because it’s measuring the current number of American-born residents of each country, compared to the residents from said country in America.
As of what year?
Edit: id also like to point out there are diaspora maps for time frames, so just posting a map with that word is as best trying to misleading or make a statement. Otherwise, that information would be freely available. That’s how data works.