Hello Steven
As you can see, ‘Sonar way’ built-in quality gate is focused on New Code only, and the Projects page will show you the ‘Overall status’ perspective by default.
If you select the ‘New Code’ perspective or go to your projects page, you will see the ratings assigned to your project New Code, the ones that are passing the Quality Gate criteria.
From your post I understand you might not be too familiar with the Clean As You Code methodology and would thus suggest that you read the Clean as You Code: How to win at Code Quality without even trying post before you go to the corresponding documentation page in order to configure your SonarQube project for it.
Let me know if that helped.
Sylvain