The instrument screwdrivers with the smaller handles are still made!
Good quality too!
The others are made from Tenite (a DuPont material I believe) and in my opinion are the best drivers Snap On ever made!
The material is marginally more brittle than the later styles (I wouldn't say exceptionally brittle) but I reckon the shape is perfect for general use (not maximum torque, just general use)
Unlike the later styles, if you get a few scuffs on these, you can just sand 'em down and polish them! Provided there's no major damage they can be restored to pretty much new condition (less the markings, which you don't have anyway)!
The other guys are right, probably from a contract or somesuch! Loads around, but equal quality! Good find!