I get a little confused of this. Looked a little on tubes some months ago when I considered upgrading my old triod amp. I think it is good, but not enough power for my speakers. Could be excellent for AKG K-1000, especially after some tuning. But that is a coming project.
Thought NOS is tubes that are not longer produced as Siemens, Philips and Mullard (although there are equivalents made by new companies). The New in NOS is only that the tube is unused or little used. You don't get these tubes in new amplifiers, with few exceptions. Musical Fidelity made a limited edition of amplifiers based on the Nu-Vista tube. I really don't understand where all of these tubes come from except military supplies that are successively sold out. Maybe, some can be found by hunting through old radios, amps and the deepest corners of supplies.
This breed must disappear, except some EXTREMELY expensive samples.
Is this a problem? I don't believe so. Some say that NOS is better, some it is hype.I have not listened to these NOS tubes but know of no other 40 years old electronic component that is superiour to current ones. Resistors, capacitors, transistors, tweeters, cartridges, turntable motors?
It seems like the death of the turntable. In 1994, Robert Harley in his excellent guide to high-end audio advised to buy a really good turntable rather than upgrading later. Because this might be you last chance! I don't blame Harley as noone can foresight the future, but this was evidently wrong. There is an abundance of both good, low priced turntables as well as expensive high-ends. And cartridges too!
There is also an abundance of tube amps and other tube equipment. If NOS are better than new ones and eventually will vanish, I think improved new ones will appear. As long as there is a demand for tube gear.