One thing that we emphasize when talking about our database is what it really represents. While we catalog tens of thousands of vulnerabilities more than any other database, we are also upfront that there are still thousands, possibly tens of thousands more vulnerabilities that are already public, but just haven’t found their way into a VDB yet. These are not 0days, vulnerabilities that exist, have been discovered, but remain private. These are public and out there to be cataloged. We have been actively scouring a variety of resources to catalog those vulnerabilities over the last ten years, and we have a long ways to go.
Earlier today I saw an image that really visualizes this point on Twitter via @nitr0usmx. He indicates that the image originates from Fuzz Testing for Dummies by Art Manion and Michael Orlando. As you read about vulnerabilities and patch your systems, remember the bigger picture.