Is there a website to read about them?
I think you are probably safe to assume that there won't be that much difference if any at all. The greater issue may be whether or not NOS has a more complete vacumn in the first place and what effect that may have on the sound of the tube. And I don't have a clue how you could ever ID that difference. Interesting thought though.
Believe it or not tube shelf life can be as high as 100 years...that is not a typo! I would keep them in their original boxes, in a cool place where they are not subjected to possible bumping, banging, or droping. The 'silver cap' inside the top of the tube is a substance called 'getta' which is designed to capture and hold stray atoms of Oxygen, Nitrogen, etc., which may effect the performance of the electronics. If the silver turns to powder and flakes off your tube might have sprung a leak! I my opinion tube design was discarded premature...I don't believe the engineers fully exploited possible designs.
The line I've always heard is that it's the useage of the tube that causes it to degrade. Keep in mind that there are antique radios with tubes that are fifty years old that still work--at least enough to prove that Grandma's 1933 Philco can tune in the glories of AM talk radio. (I wonder what would Grandma think of some of the things they talk about on talk radio?)
Quincy...As you say, vacuum tubes generally include a "getter" to "get" stray atoms of gas that leak into the tube. However, I think that the getter needs to be hot to do its job, which means that the tube should be operated. Early vintage CRT tubes used to fail easily due to gas. A TV that was stored unused for a year or more usually meant a ruined tube. Recent vintage TVs don't seem to have this problem.
Ed_sawyer...A military equipment that I was involved with had a vidicon tube, and to maintain its life we had a requirement to turn on and operate spare units for 30 minutes every 90 days. This was to get the getter hot. I guess there may be different kinds of getter.
Early vintage TV tubes (CRTs) definitely had problems if stored for a year or more without operation. Of course, a CRT has a lot of glass area for leakage to occur.