I had a box of attic junk that had about 50cd-r discs with Various bits of data. Mostly old Linux ISO's - I can tell you that over ten years in an attic wiped Sony discs to nothing, damaged Maxwell discs and made Memorex discs auto eject. Various floppies from 1990 or later stored in the same box read just fine... So that blew my mind.
Cannot agree more. I had around 300 CR-R/DVD-R and a couple dozen of DVD-RW disks, of various brands, mostly Sony, Verbatim, or Maxwell. Although those claimed to be able to sustain 10+ years, some even claimed to endure 50+ years, quite a few started to fade in 3 to 5 years and most of them failed when I last check after around 8 years. I might be able to recover a couple of them, but I would say 95% of them were long gone before I checked. It was quite a pity that some videos I archived on those disks were permanently lost. I knew those optical drives could easily become unreadable if the surface got scratched but I did not realize it could just fade away or I could have just keep those I don't want to lose on HDDs. I did not got a chance to check my floppies as my floppy drive got busted and there was really neither much point to get a new driver nor I could easily get one. Data on my HDDs is just fine, even after almost 15 years not been powered on.
Now I'm getting curios on how long my data can retain on a SSD without powering on it...
I had a few dozen CDRs from a couple different manufacturers that I used as backup discs that sat in an air-conditioned dark closet for about five years. None of them were readable without errors. Today none of them are readable at all.
I think the parent commenter is making a funny. CD-Rs were often unreadable within a few years even under ideal conditions. Put one out on your desk where sun from a window can reach it and you might not be able to read the disc in a few months.
You want something cheap, inert, resilient, and unlikely to be repurposed for any other use.
QR codes are one of the first sort of barcodes to come to my mind for storage; but I'm reminded of how poorly they encode text compared to analog characters on a printed page. The printed letters are also a technology that is already known and self documenting. If you can understand the content there's no intermediate representation.