How long do CDs and DVDs last?

So how long do CDs and DVDs last? Sometimes things on the Internet take on a life of their own. That's why I occasionally engage in what is often called "egosurfing" -- that's searching for your own name in Google or other search engines. It can be done by authors to check on illegal use of their material and I've known several fellow writers who have found their words in places where they did not expect them. In my case I have a lot of content that is offered free for non-commercial use provided it includes my byline and a reference to either a specific book of mine or to a more general description of the kind of books I write, (Googling my name will show that a good number of computer user groups have used my articles with correct attribution). It is seven years since I wrote an article for the Melbourne PC User GTroup, the largest computer user group in the world, asking "How long will a CD-R last?" It received widespread republication worldwide and many crosslinks to the original article at http://www.melbpc.org.au/pcupdate/2106/2106article14.htm Then it started to take on a life of its own, and as the article got older I'd still get fairly frequent emails from all over the world with questions on whether the conclusions in the article were still current. I had to reply that while I could not vouch for most, one of those conclusions, that most problems with CDs and therefore most likely with DVDs too occurred while they were being written, rather than in their storage, did seem to be still accurate. Only last month I was given a CD by a relative which was supposed to contain a mass of family photos. It contained nothing. The person who gave it to me was reluctant to go back to the person who had produced the CD but eventually, after getting several people to try it, got another copy -- which again did not work. I suspect that many backup CDs will have the same problem. They will fail when needed a few weeks or months later but not because of any gradual failure in the material. They were not created properly in the first place. However, returning to my theme, my latest find on Google was that the article is referenced as a source in a new book, Robots in Space: Technology, Evolution, and Interplanetary Travel by  Roger D. Launius and Howard E. McCurdy, published this year by Johns Hopkins University Press. You'll find it on Amazon. The real question is, as my article was really just a layman's summary of published research and manufacturers' claims around eight or more years ago, why has no one produced similar advice brought up to date?