I hear once they get beyond 350 or 250, whatever the build is supposed to be, they will not have a serial number and 1 blade will not have the dark etch.
I have a GEC Sheffield Tobacco, a GEC Rogers Green Tea, a Northfield Burnt Stag, a Tidioute Bocote Wood, all 73 patterns and a Tidioute Chocolate Bone 23 pattern.
All 5 of these unseialized knives are from 2006, and I think will be more rare than the 2007 knives. I doubt there are many 2006 unserialized knives out there.

I was darn lucky to get these.