Schl=20 does not include certificates. The actual paper survey goes from "one or more years of college credit, no degree" as you said to "associate's degree". It stinks, I know. For my work it would be helpful to know about people with certificates because currently a welding certificate would be treated the same as a college dropout.
I should add, I have a paper survey because I was selected to complete the ACS a few years ago. It was a little sad how excited I was.
[Updated on 10/22/2013 1:41 PM]