somewhat in the line of JoeMike's post, computer optical drives can fail in very specific ways. It may stop writing to CD-Rs. Or fail to read dual layer manufactured DVDs. And work totally fine in all other respects.
I have a stack of discs at work that i use to test drives when people inevitably check in a machine saying "the optical drive doesn't work" and don't tell me what they were trying to do. I have a manufactured CD, DVD, dual layer DVD, as well as burned CD, DVD, and DVD-DL. Those catch most read problems. But I'm not going to try a bunch of test burns, they're going to have to tell me if they're having burning problems.
