Tube Shelf Life

I have purchased several NIB Electroharmonix tubes. These are the new variety and not NOS. Does anyone know what the anticipated shelf life is on these newer tubes or any reason to believe that they will degass or otherwise degrade faster than NOS from 20 or more years ago?
Is there a website to read about them?
I've been told that tubes don't deteriorate (if unused) over time....
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.
They should be fine.
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.
What can go wrong with something sealed in a glass tube?
The pins may corrode over enough decades but that is easy to fix.
For cool tube reading, try and be ready to read loads on the history of tubes.
If your old tubes start passing gas, believe me, you'll know it if you're in the same room. Just keep them away from the dried fruit and legumes and you'll be fine.

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.
Getter material doesnt' need to be hot to do its' job.

Old tubes can work a long time. In my main rig, the preamp is using tubes from the 1920s, and the ones in the amps are from the late 20s through 1940s.

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.
As always, much appreciation to all those that provided insight !