Re:Western Digital unveiled its SanDisk 1TB SDXC card prototype
by ghshephard on Wednesday September 21, 2016 @02:15AM
(#12545829)
Most Optical Media degrades almost immediately, depending on storage environment, lasting as little as two two years before they start to degrade/aren't readable (depending on the dye and substrate). The MDISC is archival format - designed to last a minimum of 100 years when stored under reasonable conditions, and up to 1000 years if stored in archival (cool, dark) environments.
They are essential carving physical holes into a stone like substrate.
The verification tests are really quite impressive: http://www.esystor.com/images/China_Lake_Full_Report.pdf
It turned out to be totally fine, as far as I could tell. None of the early data had SHA/MD5 sums (I added this later), so there's no guarantee the earlier discs weren't somewhat corrupted, but they were definitely readable.
Back then, I had assumed they wouldn't have that long of a life, but as you seem to have found, and I discovered, once written, optical media seems to have a very long shelf life.