NOS, how often is this term used correctly?

I havent seen this as much here on Audiogon, but on Ebay the term NOS in regards to tubes, whether naively, maliciously, or ignorantly is misused. I have bought tubes advertized as NOS which came back testing as "replace" on my tube tester. DO people there realize that NOS, means NEW old Stock? Unless someone knows the source where the tube came from, ie, sitting in a box in the back of an old tv shop or a bulk military purchase, I dont know how someone can say a tube is NOS.