The tools results are based on the best ranking websites that can be found in Google. There might be a few reasons, why there can be a difference between the sites listed by us in the Content Success tool and the ones you would find when searching directly on Google.
Google personalizes the search results depending on more than 200 factors. So maybe what you see is something different then what we see.
The second option is, there are technical difficulties while analyzing a page. In this case, we can not fetch data from this site, and therefor will not take this page into account.
If you want to check whether your website is optimized for a specific keyword already, insert the website into "Compare with URL" or copy and paste the websites text into the "Text-Assistent".