I take it our hypothetical system would not simply assume that diaries are accurate records; they would (so to speak) ask the question "how likely is it that any given person would write this diary entry?" which is not at all the same as the question "how well does this diary entry, taken at face value, match the actual life of this person?".
This raises the question: Is it possible to deduce the correct person without creating conscious simulations of possibly very many people, which raises ethical questions.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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