Yes, I can clearly hear two different sounds there. But it’s an artificial environment–words don’t sound the same when there is a special emphasis on clear articulation.
It also still doesn’t quite quite answer my question (which I see now was somewhat ambiguous). I’m not claiming that unmerged speakers don’t produce two different sounds for the two words. It’s whether there are two unambiguous sounds there regardless of context and the speaker. Perhaps there’s just one vowel sound with a broad range of possible pronunciations, and one man’s cot is another’s caught.
I don’t think any native English speaker could ever fail to distinguish not from note, regardless of who’s speaking or the context. The vowels are just too different. Is the same true of cot/caught?
Another question: what do unmerged listeners hear when a merged speaker says cot? Always one or the other, or is it random, or do they realize that there’s an ambiguity at all? Might shed light on the first question.