As for tape degradation, the SSS (sticky shed syndrome) was a major
problem on Ampex 406/407, 456/457, scotch 226/227, and a few others.
After
Quantegy stated they had fixed the binder problem I bought 4 new cases
of 456 with the new and improved binder. They were good for the first
few years, but after that they slowly degraded into sticky shed just
like the earlier stuff. Ended up pulling the flanges off and tossing the
balance of the remaining tape into the trash.
I bake tape for about 3 hours at 140-150 degrees if there's any question about age or storage (and these days there usually is). This will cause the moisture to exit the tape and it should be good for a few months. It helps to store the tape in a plastic bag with a packet or two (more if its 1/2" or 1" tape) of silica gel to absorb moisture. Its better to store the tape in the attic rather than the basement! We remastered an LP where the artist ('Spider' John Koerner) did exactly that and the tapes (recorded in the early 1970s) were immaculate- no shedding and no need for baking.
it is my understanding that most of the old tapes have been digitized.
Correct me if I am wrong but digital storage is certainly more robust.
Once in numbers that "sleepiness" can be corrected with very modest EQ
as well as doing neat stuff like getting rid of the tape hiss.
Some tapes have been digitized. Many, possibly most are missing because studios sold them off or sent them to landfill. Digital storage is less robust than LP, unless the digital storage is constantly moved/backed up (which means electricity is involved for the period in which the recording is stored); if analog tape is stored properly (see above) it can last decades, but its rarely treated properly. You can't correct that 'sleepiness' with just EQ; you need a bit of expansion (as opposed to compression) and you can't do anything about the loss of detail. This is all why original LPs are usually the best 'record' (if you'll pardon the term) of an older musical event.
This is according to research done by the Library of Congress when deciding upon their long term archive needs.
That study was done sometime in the 1980s if memory serves. What they found was that laminated media (magnetic media and CD) had lifetimes in decades if stored properly (months or years if not) but amorphous media (LPs and the stampers that made them) could last centuries. The study did not include any kind of solid state media like thumb drives.
