David - I've been in contact with Rick Bowles by e-mail about this knife and he has confirmed the provenance. I'm hoping he'll write me a formal letter but I do have copies of the e-mails and photos.
Your logic is that it is a Model 1-6 (with the Model 1 "top" not being added to a Model 5 per Shop practice or policy).
Which makes sense because why add the divot that characterizes the Model 1 to a Model 5 anyway?
And it is left for us to assume that somebody wanted Thumb Notches added into the Model 1 divot. Perhaps that somebody "thought" that the divot plus the notches would provide improved purchase for the thumb or finger that is placed forward of the hilt.
Since it apparently has never been a "user," perhaps the original buyer simply wanted something that nobody else might have ever ordered, but that person probably did not foresee that he would create a mystery to intrigue and befuddle us of the future!
Larry
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Larry W. Williams RKCC #CM-041 ABKA #046 RKS #1246
The "divot" is a finger relief. It is designed for your forefinger (pointer) when grasping the hilt for edge up fighting (Bo's preferred style) offering a more comfortable grip. The top quillion of the hilt goes between the forefinger and middle (bird) finger.
Just received this one in the mail. It had a fairly rough handle with one big protrusion. It also came with a mediocre factory edge. So, after a half hour with a file and buffer, and another half hour on the stone, I now have a fantastic 5-4 that I have carried the last 4 out of 5 days. (Went to NYC on one day and they still don't understand knives)
It is a wonderful size and shape and fits my hand like a glove. Also received a nice vintage 5-5 that I will post pictures of later.