Accuracy is relative.

Do you have access to data that is more accurate?

In the end, the most accurate data on mortality rate will be determined only after the virus has been contained.
So the question at this point is 'which data is most likely to be the most accurate'.

China has ~80% of reported cases, so It seems that the WHO-China Joint Mission report, and the Chinese CCDC report , both released a couple weeks ago, is the best we have at the moment.