For anyone following this discussion, I’ve found the problem. Dorico’s MIDI import logic filters out what it considers to be empty tracks (since many real-world MIDI files have tracks with no data that are just used as labels, or are just part of the musician’s new-project template). If there aren’t any notes, then it’s considered to be empty. So in this case, if you just add a single note at the start of the file and then drag it, then the CC values are imported successfully. I might change how drag and drop of MIDI works in cases like this because I think it could be useful.