Imo, something isn’t a myth just because it’s hard to prove definitely due to a near infinite amount of samples. By the same argument you could pretty much discredit most knowledge. Dna being unique or the speed of light because we haven’t tested all individual photons.
Its healthy to always acknowledge the possibility but if there’s a mountain of evidence pointing one way, you kind of go with what you have.
Obviously though, it’s insane we don’t have better standards. It sounds like most times, it boils down to a judgment call from an expert and that is clearly not okay.