As someone who is trained in surgery and a little bit in forensics as far as university goes I´d like to throw my hat into the ring and share my thoughts. The following is just meta-medical smalltalk.
Looking at the collegues Rey drawing of Van Goghs "ear-status" one can observe a concavity towards the head. This can most probably be accomplished by pulling the ear to the side and then cutting. A sword-strike with that navigation through tissue and creating such a concavity would not only be fantastical, the blade would be simply stopped by the skull and get stuck. The authors of the book claim on their website it has been a saber by the way.
I´m indifferent to the outcome of this research project but I think it won´t be possible to back this hypothesis up unless some notebook turns up. The projects website and it´s data is a little off from scientific standarts. In my opinion, it´s about selling the promoted book
https://vangoghsear.com/index.html