Magnetic recording tends to be resilient. I still have some 7inch (yes 7) floppies that
were still readable last year- most without even seek errors.
Unlike some 3 year old DVD's that dont even start up in the drive.
In my experience:
If you have a serious archive never used DVD/CD/BluRay style technology. It rots.
Any recording technology rots; perhaps the best solution is to make copies to new media every few years. Of course, this assumes that Adobe will still be around in 20 years so that PDF documents will still be viewable on our shoelace-tip computers that project a 57-inch holographic image.
The longest-lasting medium for preserving documents still seems to be chiseling them in stone.