It looks like I'm late to the party here! I have kept a little list of 7E SBTs and to date I have identified 21. These are guns that were for sale over the years or were otherwise referenced here and there. I have serial numbers for some, but mostly not. Generally, each gun is fairly distinctive because most have been messed with, but that is beside the point. I would imagine that there were more NIDs built up as 7s than Knicks, and just knowing that there are probably at least a couple dozen Grade 7 Knicks out there, that 22 number has to undershoot the mark considerably.