Remember that this is about a coin flip that is in the past and known to be in the past. And that the future duplicates can remember everything their past potential-non-duplicate knew. So they might believe “now I’m not sure I’m not a duplicate, but it used to be the case that I thought that being a non-duplicate was more likely”. So if that information was relevant, they can just put themselves in the shoes of their past selves.
They can’t put themselves in the shoes of their past selves, because in some sense they are not really sure whether they have past selves at all, rather than merely being duplicates of someone. Just because your brain is copied from someone else doesn’t mean that you are in the same epistemological state as them. And the true descendants are also not in the same epistemological state, because they do not know whether they are copies or not.
Remember that this is about a coin flip that is in the past and known to be in the past. And that the future duplicates can remember everything their past potential-non-duplicate knew. So they might believe “now I’m not sure I’m not a duplicate, but it used to be the case that I thought that being a non-duplicate was more likely”. So if that information was relevant, they can just put themselves in the shoes of their past selves.
They can’t put themselves in the shoes of their past selves, because in some sense they are not really sure whether they have past selves at all, rather than merely being duplicates of someone. Just because your brain is copied from someone else doesn’t mean that you are in the same epistemological state as them. And the true descendants are also not in the same epistemological state, because they do not know whether they are copies or not.