Knapp over grind or grind over Knapp. I know they would grind to set up a dull platform on the edge to grab the material to be driven off. What little I know and its not much but I see grinding or dulling also after knapping. I have a couple of microscopes and have been trying to figure this out myself. What I see is sharp areas from the percussion or pressure flaking and then it appears to be ground down. I assume for some type of hafting and usually towards the base. Sometimes it tumble wear or water polish, but that is exhibited all over even to the point of mistakenly looking like a tool. Those breaks appear to be clean off the edges while a pressure flake shows a exact downward/sideways removal.
I wish I also understood this more. Very nice heavy duty.
Great topic for the experts and knappers. The knapping section above has some very talented people in the section above artifacts and understand the principle much better that I. Thirty(8?) also seems to know about this
HH
TnMtns