Hello Thor,
sorry for my late reply. I also don't have any academic research/opinon for my point of view. My position is based on facts like explained from Jean. I also refer you to the book from Wolfgang Schilling who is a friend collector from me. Sadly it will be difficult to get the book, the edition was very small.
A 100% safe result will be possible only by DNA anlysis IMHO.
Regards,
Detlef