It could be a question of soul distribution, though; if you can only have one ghost in each machine, and there's the potential for a spacefaring civilization to

It could be a question of soul distribution, though; if you can only have one ghost in each machine, and there's the potential for a spacefaring civilization to expand to many, many planets in the future, then it's possible that the 50 or so billion people who have lived since humanity's birth represent only a sliver of a fraction of the total number of souls needed to staff a well-stocked universe. So we could potentially be heavily weighted towards most people being on their first go-around if we have the potential to make it that far and souls or selves or whatever are actually scarce enough to be re-used.