I know my DS at a young age 5 had a 16 in block design that was a ceiling score because the test ran out of questions before he had hit the termination criterion for that test, or so the tester told us.

As for if those 17s are likely to be ceilings, can you ask the person who administered the test? 17s certainly can be ceiling scores but they are not necessarily. Perhaps Dottie will have more insight.