In a very real sense I think you are right. And the rule is "If you don't get the answer you want, call back." It helps to do a lot of reading, like you have done, with examples. Realizing that routing oneself via YUL makes me realize "Can I also do it via YYZ" or similar questions.

With my SIT example, the rep told me a) it was not possible to book the AS flight I needed and b) the stopover in SIT was raising the mileage needed. In fact, neither was correct. The online support department figured out how to book the AS flight I needed (to keep my connection in SEA <4 hours) and I knew once that was fixed my stopover in SIT on the return would price out at just 25K miles.