That being the case, he'd have presented his best findings, not something that proves nothing.
I was watching the Boyce video again Zoso,for the umpteenth time actually,and I paused it to look at the handle.
Now this is more a question for Jane,is the handle perfectly formed with no imperfections?
I presume the handle would have been cast and then coated with something as Bubo suggested.
Anyway,a small imperfection in the casting,eg,.a small dip may explain why the center of the top mark wasn't burned.
Another possibility may be,if Nevills head was tilted back it may have caused a crease which would explain the lip shaped burn.
Or as Bubo says,part of the coating may have been erroded.
Can you help at all Jane? Any imperfections on your handle?