I had this issue before, when importing via MusicXML, using the ‘existing instruments if possible’ option. Dorico has interpreted the first tenor in the chorus as the character ‘Elis’, who appears in a previous flow, as a baritone-singer instrument. It therefore hasn’t created a stave for me to copy Elis’s material into (it would be called ‘Côr T.1’ in the score, and I’d rename the stave which Dorico has called ‘Côr T.’ to ‘Côr T.2’). I attempted to create a new instrument myself, with apparent success, but it wouldn’t appear in the score whatever I tried. What is the correct procedure?
UPDATE - I’ve now added another scene/flow, and another voice has been incorrectly allocated - in this case to another singer who has previously appeared. But because that singer doesn’t appear in the latest scene, I don’t know how to cut and paste between staves. Ideally I’d like to see all the staves in all the flows to do this. I’ve fiddled about with ‘staff visibility’, but without success - I can’t get it to operate project-wide.