A couple of (not so) quick points.
As has been mentioned, some of this media was crap when it was new. Aging it for 30 years or so can't have improved it much. We're not talking about fine wines here LOL. I distinctly remember a brand new 5.25" floppy from INMAC fouling the heads on the drive right out of the box. When the second one did the same the whole box went in the trash. That was on my (then new) Heathkit H89 so figure late 80's. Towards the tail end of the "floppy era" I bought a white box of 50 3.5" supposedly preformated and tested disks that wouldn't hold data for a week, much less tens of years.
My mother recently passed at the well earned age of 94. In her 60's, she got bit hard by the Genealogy bug, drug my retired father to libraries all over the USA, Canada, and the UK, published two books, and taught herself computers in order to keep it all organized. In disposing of her effects, I ended up with several hundred 3.5" floppies of research notes, backups, and the WordPerfect text of her books. The relevance to this discussion is that I've been archiving the lot in order to pass it on to any of her descendants who might want it. The oldest disk I've seen so far was written in 1989. The newest was written in 2002. They're primarily from Scotch/3M with some Memorex, TDK, and Sony in the mix. Using dd under Ubuntu 20.04, I've been able to recover 100% of the contents of all but three disks. Even ddrescue was unable to do a complete recovery of those three. The good news is that the failing disks were from backup sets and she was apparently in the habit of doing each backup twice. So in all three cases the data that was unrecoverable from one set was recoverable from the other. All three problem disks were from Memorex.
