NOS is a New Old Stock, GM part, something that stayed on the parts shelf that never sold.
NORS is an New Old Replacement Stock part from some vender other then GM that never sold and stayed on the shelf.
Both are worth using if they are not rusted or have rubber in them. The types of rubber used back then don't seem to last. Also be careful when shopping, some " NOS " parts are actually returned parts that may not have fit or had some sort of defect in them. Case in point, I purchased a set of NOS tie-rod ends for my '37, they looked new and the box was in good shape, but one of them wouldn't turn smoothly. No amount of grease would free it up. When I really looked at the parts, I could see where they were installed at one time.
Joe
