Discs almost completely filled with errors. Am I doing something wrong?

[DebianDoesDallas]

I've just started using dvdisaster because I want to check whether a scratch on one of the discs of a used, commercially produced boxset, is playable without needing to watch it start to finish.

When I read the disc with dvdisaster, it's saying that the disc is entirely full of errors except for the first handful of sectors. This is despite the rest of the surface of the disc looking factory fresh, and the disc seemingly playing without issue (although I only tested the disc by skipping forward a minute, watching a few seconds here and there, and fast forwarding).

I'm running Debian 12, and I've tried using both the 0.79.5 version of dvdisaster available through apt, and the latest appimage (dvdisaster-v0.79.10-pl3-x86_64). I've tried both versions with both my old internal Blu-ray reader, and a newish external LG MultiOS DVD drive.

I've also tried scanning another commercial disc (a DVD of the movie "Infested" 2002). The behaviour is the same.

Both discs are being reported as DVD-ROM by dvdisaster but I know nothing about discs with a "c". So I don't know whether that is correct. I should mention that I have R'd the FM, and I know that DVD-ROM discs are not supported but as I say, I don't know whether my discs are being correctly identified.

Am I missing something or are the discs being ROMs the issue?