The only time this was ever an issue was back w/ CDS-200 Audio CP. We all agree that by adding CU (E32) errors and damaging actual user data (PCM) that you have a pre-damaged disc. So with general surface scratches, finger prints, dust etc. the normal ECC wouldn't work as it would w/ a standard disc.
I got to thinking about all these non-standard CP used on optical media that perhaps, since none meet the book standards (though no one but philups ever complained) that DRM may not be so good for you :sad:
General Brief Overview:
Bad Sector Based: SoftLock or freebie apps that just try to stop you from reading the disc by screwing up mode 1/2 EDC/ECC. Like CDDA it is damaged w/ E32 errors...thus if you got more errors it is possible that some drives would indeed have problems reading the disc.
Key Based: The most common SafeDisc, SecuRom etc. have a small section that the app looks for a unique "key" If you get a bad scratch on those sectors they Key may not be read properly. While the Yellowbook standards seem intact, they aren't since it's depending a such a small section which shouldn't be vital data.
DVD Video: RipGuard, Sony etc. damage sectors that aren't used at all, however their has to be some reference made to these or it wouldn't work. The question is how does the disc handle additional wear and tear on normal sectors since there is already bad sectors on there? This one may actually be safe but none of what I am saying has been tested or proved.
What's your opinion about non standard protections? Should they even use the book logos (DVD Video, DVD-ROM, CD-ROM etc.) since they are non-standard? And as I asked do they lower the actual media quality?