This is what I refer to a "dye mottling". It's a defect in the dye, and was always present. The defect existed when it was not yet burned, and was not visible. It became visible/mottled at the time of burn. This error does not appear over time -- it was always there, even if you didn't notice it. Discs with mottled dye are not necessarily coasters, though most are. Even discs that burned "fine" have horrible scan values, and it should be classified as bad media.
Over time, the dye value will shift, and this kind of media will effectively "die" much earlier than good media. How soon depends on how bad the error is. I've seen this defect cause issues within 1 year, and others are fine after 10+ years. It's not really "data loss" as such -- the information is still there, just hard or impossible to read.
Moser Baer (MBI) is a common offender for not-good dyes, and is why it's poorly rated. Though supposedly using the MCC01RG20 recipe, MBI01RG40 media was lousy. It was not as good as Mitsubishi/Verbatim. MBI01RG40 media is also from about 2004, so it's a lot older than 5 years!
Re-burn the data/video on better media.
Read through the media reviews, if you've not done so already:
http://www.digitalFAQ.com/reviews/dvd-media.htm
