Hey Jack! Good to see you posting. Sure, give me a few days. The work on that section of my book was finished almost ten years ago; I'll have to dig out my notes. That said, I believe your deductions are correct, and that I based my observation on documented knives, or on knives with known date characteristics. However, if only one sample knife was found to be used, there's always a probability that a sheath or stone could've been swapped at some point, and that would affect the dates given. I'll look into it and email you.