This Rolex just came in today. An "E" serial NOS ca. 1991, apparently new old stock, unworn watch. Note the absence of any wear under the lug (yellow arrow). Even internally, the watch looks as good as brand new however this could fool only a novice watch collector.
The auto rotor assembly reveals a different story- the watch is long time overdue for complete overhaul. Note the 'saw dust' all over the rotor bridge: this mixture of dirt, gummed-up oil and metal particles would kill the watch in just few months.
Beware of NOS ! All NOS do need complete overhaul before they could be worn again. Buying an expensive timepiece from a fellow collector could be problematic, even when the seller is completely honest. "Never worn" or "worn only on special occasion" usually means overdue for an overhaul! If you really like the watch then offer the seller to split costs of having it overhauled.
[Q]: What is the difference between BNIB and NOS?
BNIB (Brand new in box) and NOS (new old stock) are commonly abused terms in watch trading. In my books, BNIB means only one thing: a brand new in box, purchased directly from dealer, where the definition of a dealer is "person who sells watches for a living". The very moment you leave dealer's shop, it is no longer BNIB.
If you are buying something from someone who is not a dealer then you are not buying BNIB. At the best it is LBNIB (like brand new in box) and you are not necessarily the second or third owner either. NOS apply to OLD / VINTAGE unsold watches that are no longer in production. Unfortunately, this means different thing to different people.
In this particular case, the watch was possibly wound manually or was sitting on watch winder, or worn on a different bracelet or leather strap. Maybe just for a day or two. The point is this: it EXTERNALLY looks like NOS yet internally something has happened in the past to cause the wear as shown on photo.