First of all, lack of testing and government denials that there is a problem here been a hallmark of the response worldwide. It is hardly a conspiracy theory to say that it happened in Japan as well.
Secondly for a couple of weeks now I've been running across articles of the form, "Japan should have had a problem by now, why are they an exception?" Which is more likely? That they were an exception until now, or that the Olympics provided extra motivation to stonewall?
It is clearly not proof. But extra motivation to fail to try to detect their own problem combined with reason to doubt their version of reality (in the same way that happened over and over again elsewhere) makes my estimate of the conditional probability very high that their government was simply a bit more deliberately blind than elsewhere.
And, as with everywhere else, the cost will be dead citizens. Only the further you let the problem go and the older your population, the worse it is. Japan has the highest concentration of truly old in the world. And may have let it go longer than anywhere else. The result? The final body toll won't be pretty.