One thing to keep in mind is the false positives that seem to be coming out which get retracted or the cases that go from unknown contact to known days later as happened in NSW with one of the weekend cases. It makes the news that day but the retractions don’t.
A false positive rate of <1 in 10000 is pretty good.
They are testing huge numbers so obviously there will be hiccoughs, most of the world would consider these utterly inconsequential. We saw the consequences here after the sad death in Queensland.