There are probably regional differences when it comes to defining what the term "NOS" stands for.
In many parts of the country it stands for "new old stock" that hasn't been used. It's a hoot to see bikes being offered for sale in unopened crates that some bike shop owner reportedly kept in inventory for over 30 years. On Craig's List in NYC the term often stands for "nasty old s**t" (synonymous with POS). Ad titles often read like this .... "yOh, YoH, NOS oLd sChOOl sEeRs 10sPd cHeCk It oUt!!!!! $399!!!!!"