The likelihood of having a DVD actually degrade is about the same as buying a winning lottery ticket. So don't lose faith in the format as a whole.
However, there are many reasons why a DVD will not perform as well as desired, and it can almost always be attributed to the media in use, the players/readers in use, and the method of storage.
So let's start from the top.
- What is the brand and media ID of the discs?
- What are the brands and model numbers of the DVD players or DVD recorders used for testing the disc?
- What is the manufacter, brand, and firmware type of the DVD-ROM and/or DVD burner used for testing the disc?
- How were these discs stored? Give a much information as possible (brand of items, where purchased, etc).
- Are you a smoker? Be it cigarettes or some other guilty pleasure of choice. If so, do you smoke indoors, or is there a heavy smoke smell from smoke that follows you back inside when smoking outdoors?
Optical media is susceptible to three main problems:
- Diffraction of light. A typical cause is scratches, including ones so small the "naked eye" cannot observe them.
- Poor reflective properties. Some disc's materials do not adequately reflect light, so the data cannot be read, or can only partially be read. As lasers age, poorer media quits playing first. Pressed media generally can be read the longest, as it has better reflective properties than dye or phase-change materials.
- Poor lasers. Unlike media, lasers can and will die in a few short years, especially on lower-cost equipment. Optical electronics are also extremely susceptible to damage by smoke, and it's no wonder smokers are the ones found with the most failing DVD equipment.
Another item of note is testing methods. A great many people have not run a full battery of tests on discs, relying on playing media, or on those near-useless PIF/PIE/PI/PO tests that are found in "scanning" software. Those are known to be unreliable outside of a pro lab, due to the many variables that exist in testing. Playing a disc will heavily rely on the player's error correction, so you won't actually get a good handle on the data's integrity.
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From the details I've gathered so far, you're already suffering from poor media. Ritek does not degrade as much as it's difficult to read, even under optimal conditions. Of all the media that exists, it seems to have the poorest reflective quality around. It's not "dead" as much as it's just hard to read (and it always was -- but your equipment ages too, which makes it appear that the disc "died" on you). If you're lucky, it might just be a lot of dust has gotten into your player.
BeAll media is just as bad, if not worse.
Neither of them would be considered "top quality" media, and never have been outside of a few user forums online (the blind leading the blind, if you know what I mean). It's a shame those sites mislead so many folks. High quality media is and has always been discs manufactured by (not branded by, but MANUFACTURED by) Taiyo Yuden, Mitsubishi/Verbatim, Maxell, TDK and Sony. These days, TDK and Maxell is almost impossible to find (again, the manufacturer, not the brand). Sony is only good from Taiwan and Japan, not Malaysia. Verbatim is easy to find, and is often on sale. Taiyo Yuden is only available online, and you only want to buy from a reputable dealer (supermediastore.com, meritline.com, rima.com, gotmedia.com) to avoid fake TY discs.
In terms of archives, it's smart to use multiple types of media (often even stored in multiple locations) to avoid loss. A good hard drive (Western Digital or Seagate manufactured drives -- nothing else!) full of images is a great idea. Some good discs at another location is great. And even a second set of discs, from another good manufacturer, is suggest at another location. Maybe even put on set in a fire safe somewhere, or a bank security box with other valuables.
I see you've been buying a lot of Mac-marketed brands like Formac and Lacie. Honestly, it's a waste of money. Those devices can sometimes use sub-standard internals, or they'll use the good internals at a crazy-high price compared to buying the manufacturer's self-named brand. Pioneer/Samsung/Sony burners and Seagate/Western Digital hard drives work perfectly on an Apple machine, and are much better in terms of reliability. The gear in use might be partially to blame too.
Computers rarely know more than humans, so the "best" speed in Toast may not actually be the best speed. You'd do best to set the disc speed based on the disc. If you've got 16x Verbatim media, burn anywhere from 4x to 12x. Odds are those Ritek and BeAll media were burned too fast, which led to first-unnoticed errors (or imperfections) that have always existed.
Your current discs may still be salvageable on a good drive. I have several BTC drives, known as some of the best readers around, that are good at reading stubborn media. Only a fully-inoperable disc ever fails to read on my drives. They would need to be ripped, and then re-burned to a good disc. I can usually recover about 80-90% of "dead discs", because most of them are fine, just hard as all heck to read.
So that's probably where you are. I don't even know that I need the answers to the question above, but it might be good to know. Odds are that several of your drives being used for testing are the same brand or even same model of drive in various pieces of equipment. So they'd all give the same performance for reading a stubborn disc. RITEKG04 and RITEKG05 media have been some of the worst discs, when it comes to reflective quality, so check the ID on those discs.
Hope that helps.
If you'd like me to try and rip/re-copy some of your media, I don't charge a whole lot for that service.