I'm skeptical whenever I see a teardown like this which fails to mention that the offical case counts have all the same problems. Maybe we should dismiss this paper - but that means committing ourselves to radical skepticism about the prevalence, not going back and believing the numbers printed in the news.
PCR tests are asymmetric. Positive result almost certainly means that this person has the virus, but negative result might mean a number of things. Bad swab (less than 3000 virus copies), temporary remission (Korea has at least 160 such cases by now), etc.
Test kit availability adds another layer. At some point New York had 200 confirmed cases, and two weeks later 400 deaths, yet CFR is unlikely to be as high as 200%.
So yes, all statistics should be taken with a grain of salt, but magnitude and direction of that grain may be different.
