I think 100% certainty that a node is the originator of a request is not necessary for most purposes. If you are thinking of a court case, then maybe, but only if there is no corroborative evidence.
And in other situations where people might want to use a darknet (e.g. a repressive regime) a few false positives aren't going to bother anyone concerned.
And in other situations where people might want to use a darknet (e.g. a repressive regime) a few false positives aren't going to bother anyone concerned.