NOS stands for "New Old Stock." When a watch is described as in NOS condition, it refers to a timepiece that was probably put away for decades and has never been worn. However, over the years, it may have been passed from one collector to another, but as long as the new owner keeps it unworn, it can continue to be described as NOS. It may have been tried on just like those display pieces in a watch shop. But one thing is for sure is that a NOS watch is not mint. Most have been put away without protection (such as inside their original box), so expect the case and crystal to show minor light scratches here and there. Some will naturally patina or produce age spots depending on the dial material or type of luminous/paint applied on the dial and hands. But, at the end of the day, a NOS watch's condition will differ from a used piece in pristine condition or a timepiece with a case polish. A long-time collector will be able to differentiate them apart.
 
Here is an outstanding vintage NOS 1950s Technos Lyx watch—factory original in excellent condition—fully serviced Techno calibre F391 manual wind movement.  This model originally came with an unsigned crown. The case is made of gold capped over stainless steel and remains in excellent condition. The case model is 2580357 and measures 33mm in diameter, excluding the crown by 41.5mm from lug tip to lug tip. Original metal case gasket. It will come with a NOS 17mm suede genuine leather strap that is probably original to this watch, and the buckle is original. The wrist size in the photo is 6 inches.