Safe to say, Tunes knife came after Lt. Zacharias', and the Lt's last requested knife is completed 6 Jan 1943 ( As I interpret Gaddis), that's what made me think the 6 month time frame between the total of 4 ordered was devoted to that design, of course, as the production of these 4 knives may have occurred over the course of considerably less time, changes could come about simultaneously. Establishing the link between Tunes knife, and the Zacharias, could be the key factor in nailing this down, I suppose