Thanks, johnmd.

My take on this is:

If you pass the sha1sum tests, you know your files
match what LinuxMagazin meant you to have.

If you pass the testcd tests, you know your files
match what Klaus K meant you to have.

If KNOPPIX/KNOPPIX fails testcd, there is a flaw in it.

I've managed to get some miles out of a flawed LiveCD of
my own making, but that's asking for trouble.

I'm like you, there's a lot in the DVD I'll never use.
Just don't get comfortable with a flawed system.