My expectations are that an "NOS" tube will test the same as a new tube would and have a long life. I have noticed that some dealers are now selling tubes with very little flashing/gettering which indicates to me heavy usage. Others are just stating that tubes test "as new", which as Thorman said, is really the most honest sounding representation anyone can make.
I have often wondered how a dealer can have very similar appearing tubes and call one batch, "used test new", and the others as NOS. It is unlikely these days that anyone can source these precious old tubes in sealed cases that came from the manufacturer. The only time you might see that, for the most part, is with tubes that aren't used for audio.
BTW quietude while a reasonable expectation is not guarunteed by being NOS.
I have often wondered how a dealer can have very similar appearing tubes and call one batch, "used test new", and the others as NOS. It is unlikely these days that anyone can source these precious old tubes in sealed cases that came from the manufacturer. The only time you might see that, for the most part, is with tubes that aren't used for audio.
BTW quietude while a reasonable expectation is not guarunteed by being NOS.