Sorry couldnt be of more help stormalong, I don't know if you know Mike O'Connor, he is a bard of the Cornish Gorsedd, He has done a huge amount of research into early Cornish Music and Musicians, he may be able to help you more, or know someone who can - if you'd like his e-mail address I could pm it to you, with his permission. Let me know.
Regards, Lucy