NOS is a commonly misused phrase.   I'd like to clarify a few things about NOS.

NOS means New Old Stock  which means a it is a new parts, not always perfect, not always shiny, not always show quality.  You need to keep this in mind.  NOS parts especially during the 2nd World War used a very poor quality material so they show it. Chrome pieces are not shiny, sheet metal rusts etc.  NOS means just that, new, never used and that is all.  Don't read into it or expect show quality.

NOSR means New Old Replacement Stock.  That is new parts that were not made or marketed by the original factory.  An example would be a headlight swith sold under the NAPA name.  That would not be NOS it would be NORS and thus not as valualble.

The yellow box lenses that are so many times sold as NOS are not.  They were made by Glow-Brite and are a form of NORS.  They are great for daily drivers but the lens does not say Guide on it so it is not NOS and thus sueless for show vehicles.

One last thing to conside when thinking NOS.  

Some manufacturers made their parts for more than one car manufacturer.  So when these parts are listed as NOS they truly are NOS even though they don't seem to fit the car make.  Some examples are Trico made wiper parts for all make cars, GM, Ford, Chrysler, etc.  Foxcraft made fender skirts for all makes of cars.  They did market fender skirts in GM boxes and alike but to my knowledge practicly all fender skirt were made by Foxcraft. Delco made there products for all make cars.  Get the picture.

I hope this helps.