As delta says (in fact the researchers said 4-5 years) don't wait because once it has gone............................the recommendation was also to either back it to hard or cloud as well.
I think it is appalling that DVD disks are so bad. The BBC (it ran on 'Click' as well) reckoned that even 'top' grade disks had bad batches. Why is it so difficult to produce quality?
I found a few DVDs that would just not read after 2 years a while back. Files appeared to be all there, but it would just not put it together.