The survival rates are based on known cases, obviously because you can't know who has it without a test. But certainly there are lots of folks who must have it, never went to a hospital and eventually recovered. Based on some best-estimates-from-smart-people numbers, the death rate from this would end up being a lot lower than the flu. Granted, it does seem the death rate from the elderly and already-sick is super high, as well as the rate that one corona person gives it to 2.5 people while the flu is 1.3.