New Old Stock, old or obselent stock that dealers and parts depots at one time were begging to get rid of and now is what a mint. After it quit moving at retail or became discontinued they were dying to unload the stuff.
The owner of the business was a former Chevrolet dealer so of course he knew lots of dealers. Much of the NOS around is junk. We once bought maybe a hundred boxes of NOS Chevy floor mats from a local stash. Mostly full-size bench-seat mats in red, blue, green; obviously picked through. Still worth the $5/box but lots of heavy lifting. Later on he cooked up a deal with a traveling GM service rep. This guy would be at 2-3 dealers every week and would buy all the non-returnable parts he could find. More junk: '73-'77 bumper guards, tie rod ends, odd exhaust parts, take-off manual steering gears. We must have had 50 diverter valves, none for HP engines. We had cases of recall engine mount cable kits. Lots of switches: headlamp, wipers, ignition.
So if you hear of a pile, tread cautiously. Probably picked several times by guys that know more than you. Lots of people chasing the stuff for years. They all fantasize about the holy grail of NOS: a Chevy dealer that closed in '69 and hasn't been touched since-still a car on the showroom floor. It will go down someday and make headlines. Don't ask.