TL;DR: Writeable optical discs have a relatively short shelf life prior to use (compared to the service life of the data you record on them). Why? And how can you avoid having a stockpile of unused discs that become unwritable?
Half a dozen years ago, I stocked up on DVD-Rs and have been working my way through them without a problem. Then the other day, disc after disc failed during the writing or verification process; different brands, discs from unopened canisters, writing on different computers. I tried discs from a slightly newer batch and everything worked fine.
Data recorded on writable optical discs is often touted as having an archival life of many decades. I had incorrectly assumed that you could write on the discs at any time. It turns out that while degradation is a long, slow process, there is a limited window of opportunity to get the data on the disc. Fairly early in the disc life, the data layer materials lose the ability to record data.
There have been various studies of optical disc life and aggregations of manufacturer data. The published longevity figures typically look like these from the Optical Storage Technology Association:
Unrecorded CD-R: 5-10 years
Recorded CD-R: 50-200 years
Unrecorded DVD-R: 5-10 years 
Recorded DVD-R: 30-100 years
 OSTA doesn't list the estimated unrecorded DVD-R shelf life, but the Council on Library and Information Resources lists the same 5-10 years as for CD-Rs, so that is shown above.
Note that testing conducted by the National Institute of Standards and Technology and the Library of Congress estimate longevity at only a fraction of those numbers. The point here isn't the specific numbers, it's the relationship between the unrecorded shelf life and the data archival life.
Obviously, you can avoid having a lot of unwritable discs by just treating them like a perishable commodity--don't buy more than you can use before they go bad, and store them under ideal conditions. My basic question is can we do better than that? Two parts:
What is the nature of the problem? For example:
- Why do they become unwritable?
- Is it part of the same degradation process that eventually makes them unreadable, or is it a separate phenomenon?
- Is it a basic characteristic of all of the different dye layer materials or is it substantively different in certain materials?
- How does the writability window relate to the archival life? For example, is the time period similar across the whole family of materials or a somewhat fixed portion of the service life?
Keep in mind that this isn't a graduate course in chemistry or material science. An in-scope answer to this part will be a few paragraphs at a level intended for curious computer enthusiasts.
Does the nature of the problem provide a solution? For example:
- Is there material-specific information that can be used to better plan around the expected writability limit?
- Is there a way to store the unused discs that has been proven to prolong the writability window?
- Can we identify discs ahead of time that will have a longer unused shelf life? For example, by identifying the material, or if the writable period is proportional to the archival life, buying "long life" discs would give the longest writable period.
- If there are known factors that correlate with the writability period, are they readily identifiable, such as through visual clues or product terminology?
Note that the bullets under the two question parts are not meant as supplemental questions, which would make this overly broad. Rather, they are suggestions for the kinds of topics in answers that would address the question; i.e., they are there to provide context and focus on the intent of the question. On part 2, there may not be any solution; the bullets are intended to trigger thinking on different angles that might be useful so a potential solution isn't overlooked.