I guess the terminology is still unclear to me...

The "19" is the maximum for the subtest scaled score. I.e. -- you can't get a scaled score higher than 19, no matter how many additional questions you get right in that subtest. So whether he got "1" in level 5, or "6" in level 5 and another "6" in level 6, he gets a scaled score of 19 for that subtest. If you max out all the questions and hit the maximum raw score, meaning that you don't miss any of the questions through the end of the subtest, you still get the maximum scaled score, but you also could theoretically answer harder questions.

Which is called the "ceiling" for the subtest? Maxing out the scaled score, or finishing all the questions in the subtest? If the ceiling is going through all the questions, is there a comparable term to use to refer to having the maximum scaled score?