Just one paragraph in the text, but the hint sounds interesting: CD-RWs don't use color particles that get hit by the laser and can fade later — instead they use metallic elements that reflect light differently. These elements may not be as susceptible to environmental parameters as the color particles in CD-Rs. Something similar seems to be the case with DVDs. So it could make sense to archive on RW media. Here's more information. Here's the original article.