Compare the following situations:
- Only one group of 40 breeding pairs left. Very risky.
- A bunch of pools of left, one of them consisting of 40 breeding pairs only. Over time the small pool recovers to a few thousand people, and at that time the other pools have some accidents and die out.
The second situation was never as risky as the first. But we wouldn't be able to tell them apart from current genetics.
But if both situations have the same outcome -- everyone not descended from the 40-pair group is dead -- does it make sense after the fact to distinguish them by "riskiness"? It seems to be a distinction without a difference, as the saying goes.
In either case, the most likely outcome in the end is still that I don't win the lottery. But the chances were different.
In your analogy it's like buying 40 lottery tickets knowing that 39 of them will not win for sure vs buying just 1 ticket.
Well, what if they did?
I think that I have been incorrectly assuming that this subthread was about whether, in 2017, we could tell which of two things had happened -- either "there was a time when there were only 40 pairs of humans on all the earth", or "everyone today is descended from a 40-pair group that may have coexisted with others but for some reason those others died out."
If in fact we're instead talking about whether we can make any distinctions whatever between the two situations, even though we know now that whichever actually occurred, humanity didn't go extinct, then I retract my objections.