Yes, but with any sickness/disease. You only get tested when you're showing symptoms. My mom went to the doctor with a bad sinus infection Jan 2019 that would not go away. 1 week later she had stage 4 cancer near her brain. There are lots of people walking around with cancer, hypertension, etc... that don't know about it. Only when people get symptoms do they go to the doctors. The mortality rate has to be based on those officially diagnosed with the virus, just like any disease is.