Gary Clinton showed this knife at a lecture he gave at Blade a few years ago. It is the only three screw white Tenite in a Moore sheath I've seen in person. I would think the use of the Moore sheaths for this knife marks it as very early.
I'm not particularly drawn to m15s... much prefer m14s. But this one was cool...
I think Gaddis says that Moore invented the split back riveted sheaths specifically for the m14 and m15 knives. Heiser then used Moore's sheaths as a prototype. Randall himself was may have been involved in designing the split back sheaths for m14-15s and referred to them as "revolutionary."