I wrote a kind of explanation with IT language metaphor along of why any PCR can't be used as test - https://conspiracies.win/p/13zMZMNm90/x/c/4JEWwSmtBBL

Shortly - PCR can work as expected only if you provide a sample you need to replicate. If you don't provide it, or don't know if there is a sample to replicate, then the result have no sense at all and you could not do any conclusion based on that result.

I wrote a kind of explanation with IT language metaphor along of why any PCR can't be used as test - https://conspiracies.win/p/13zMZMNm90/x/c/4JEWwSmtBBL

Shortly - PCR can work as expected only if you provide a sample you need to replicate. If you don't provide it, or don't know if there is a sample to replicate, then the result is completely undefined and you could not do any conclusion based on that result.