There's been speculation that there might be a large pool of infected people who are not recorded in the official figures, because their infection was very mild or asymptomatic, and thus they were not aware they caught the SARS-CoV-2 coronavirus, or did not seek medical help and did not report it.
That speculation went on for some time, but the
published study from the infected cruise ship the Diamond Princess — in which nearly everyone was tested — shows that there is
not a large pool of unrecorded asymptomatic cases.
If you look at table 2 in the paper, you can see that the ratio of systematic to asymptomatic cases is approximately 1:1, as out of the 3711 people in the ship, there were total of 301 symptomatic cases, and 318 asymptomatic cases.
Although in younger people under 60, there were more symptomatic cases than asymptomatic, for some reason: for the under 60s I counted up on table 2 that there is a total of 101 symptomatic cases, but only 53 asymptomatic cases.
So this idea that there is a large pool of unrecorded asymptomatic cases does not seem to be correct.