I agree with Dopogue
N.O.S. stands for new old stock, these tubes are to start with 40 years or older. How can one be certain they are new. What is perhaps more important is how well they test as to how much life remains in the tube. Used tubes that test strong (depending on application) can last longer than we keep the equipment. I have many tubes that test strong sound great but I would never state that they are N.O.S. perhaps they should be called N.N.O.S. nearly new old stock.
N.O.S. stands for new old stock, these tubes are to start with 40 years or older. How can one be certain they are new. What is perhaps more important is how well they test as to how much life remains in the tube. Used tubes that test strong (depending on application) can last longer than we keep the equipment. I have many tubes that test strong sound great but I would never state that they are N.O.S. perhaps they should be called N.N.O.S. nearly new old stock.