Genealogy being what it is, if someone has a descendant 3000 years later, it's almost certain that everyone living at that time is a descendant. But what you'll probably hear most often in the Church is that those who are not naturally descended from Israel are adopted into one of the tribes so they still have a birthright blessing. In the source you linked, #10 has this to say: "All people can be gathered to Israel, either by direct descent or by adoption, which happens when they are bapti