In my dialect, “cot”, “Don”, and “collar” sound like “caught”, “Dawn”, and “caller”. I don’t say those word pairs differently. This is one characteristic of the Pacific Northwest Dialect. Do the characteristics mentioned in this article sound familiar to you? Some of them don’t sound like Seattle speech to me (that y-glide he describes in some of the vowels), but maybe I’m just not good at analyzing my own speech.
What I have noticed about Seattle-area speech over the years is a tendency to sound more Canadian in our vowel sounds than we used to. For example, I hear people say “sorry” with more of an “o”, less of an “ah”. This used to be the mark of a Canadian, but I hear it now in lots of younger Northwesterners. Have you noticed this too?