The issue of what is NOS comes up very often here and on other forums. I think the general consensus is it is an object that has never been sold retail and has never been used before. You see this all the time with watches. A company sells stock to a jeweler and he puts it in a safe and it falls behind something and 40 years later when he closes shop he finds the thing and sells it NOS. it could really be in terrible shape or can be in mint shape.
The bottom line is NOS as a term has nothing to do with condition. It has all to do with it's retail status.