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.
It's useless and there is no proof Covid exists.
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.
It's just there for one goal: Rationalizing policies that will soon lead to mass genocide (decade long masked lockdowns).