I have some cheap CDs with just 17 years that have oxidation dots. And a CD-R of just 8 years with a bit dots of silver missing.
When the manufactures use no protection layer or a very thinny layer, or bad varnishs, or not very pure silver, crap will happen in a short time.
The first dual layer discs have a problem on the glue, leading many ones to "crap out" in a month or two.
A single layer made with very pure silver will last longer, but even so will crap out one day.
The most durable things, in terms of stoprage, are still dried aninal skin, like some medieval books, or stone written.
The B&W photographyc paper of your grand-grandfathers can last a century or more, but the digital media of today, if not transfered, will mostly be gone in 25 yers or less.
All videos people make all the time today, the hundred digital photos people took at each trip vacation, will mostly be gone.
There is a very nice documentary of Discovery Channl about that. Not just for documents and audivisual, but even building, roadas, nearly everyting today, will last less than the traditional roman & egitian creations. The roman concrete last longer than modern concrete.
Even the TV station elemagnetic signals, that go to space, will turn to noise after few years travelling on deep space, and not even super aliens will be able to see.
Our civilization it's really a mess

Keep thinking...