With another 99 confirmed cases, the most remarkable thing about the Death Princess, er, Diamond Princess is that there are no people reported to have escaped, or attempted to escape, and at the other extreme, there is one American family who is still enjoying the stay sufficiently that they declined to be evacuated. It would seem that at the current pace, every person on board will be infected within another couple weeks.
The Diamond Princess will soon enough give us something we have needed, a finite number of cases which we can track separately to monitor progress. Currently, of 454 cases, 19 are in serious/critical condition. I think it's a reasonable guess that none of those are from the people detected in the last day or two. If they are all from cases detected a week ago, that would mean 19/135 are in serious/critical condition, or 14%.
Then, with that data, we can work backwards in China. If 14% of cases typically end up in Serious/critical condition, then if there are 11,272 cases in critical/serious condition in China, we can guess that a week ago there were about 80,500 cases rather than the 40,500 cases officially reported. That is consistent with not catching/reporting all the mild cases, but not consistent with the most extreme views on under-reporting by China. Of course, they could be under-reporting serious/critical cases, too.