A few years ago, there were (and still are a few) a few honest merchants who would label tubes as NOS or ANOS and would state the readings so you knew you were getting something with some life left in it. KCANOS is still one I recommend, but if you compare what he sells today with what he was selling 15 years ago, the inventory of NOS tubes has understandably decreased significantly. I don't recommend buying NOS today for the most part as the good ones are either very rare and expensive or you're not getting the good ones. Or both. NOS does not equate to "better tone" unless it's a known and tested "better tone". Knowing which NOS tubes will be great is more difficult than finding a good tasting wine.