vacuum tube shelf life

does anyone know how long a vacuum tube will last just sitting on a shelf unused?

the recent trouble in ukraine along with the threats of embargoes and sanctions against russia had me questioning the reliability of the supply of freshly made russian vacuum tubes. it got me wondering if i should get an extra set.

however, the tubes in my preamp are pretty new and it might be some time before they need to be changed. so any new tubes i get now are likely to sit unused for several years, possibly as much as a decade.

so will the tubes still be good when i finally try using them?

i understand that there are a lot of NOS tubes being used, most of which are old, as in 50 or 60 years old. on the other hand, the NOS tubes that are in use are survivors and i have no idea of the failure rate; how many NOS tubes have to be discarded simply because they went bad in their boxes while sitting unused. plus, from what i can tell, new tubes don't seem to be made to as high a standard as tubes used to be in their heyday in the 1950s and '60s.

what have been your experiences using tubes made in the 21st century that have been sitting on a shelf for, say five to eight years?