I've burned over 100 BluRays in the last 5 years. I've had 6 discs (that worked after initial burn, mind you) that did not work upon later access. All 6 of these discs came from the same spindle of DL BluRay discs, so there is some suspicion that I got a bad batch, but no proof either way.I recently (one to two months ago) got back like 80 discs that I gave to my friend 5+ years ago. They are all still in perfectly working order. While I like the fact that Blu-rays can hold more, there is also the potential for more files to go bad, so I stick with 4.7 GiB discs. Also the fact that DVD burners/readers are very cheap, versus needing to shell out near 100 dollars for a blu ray burner/reader. IIRC, Disc Rot is almost impossible to prove, and (IIRC) has never been observed to happen. It seems to be a myth (though Im sure it is possible). That is, IIRC. I could be wrong though. I remember reading from a hypothetical journal (they deal in tech hypotheticals/theory), and even if it does exist, it is incredibly rare.
When I say they 'don't work,' I mean to say that some portion of the contents of the disc are unretrievable. In each case I was able to see the entire list of contents, but only able to copy off a small number of the files (less than half in all cases.)
As a result of this, I've sworn off DL discs entirely. I replaced all the other discs in that batch, even though they seemed to be fine. I lost quite a few files, because I downsample everything to 480p in h.265 to lessen space requirements. Luckily, the stuff I drop to BluRay is stuff that, if deleted, wouldn't upset me terribly. I keep all the important stuff on HDD's, and make sure I've got more than 1 copy.