So finding evidence of life that went extinct at any stage whatsoever should make us revise our beliefs about the Great Filter in the same direction? Doesn't this violate conservation of expected evidence?
No, the total evidence for a great filter is conserved (lack of observable galactic colonization), the evidence merely shifts where we expect this great filter to be.
We've had these for a year, I'm sure we all know what to do by now.
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