C2 is error detection, not correction. C1 is the error correction. I think what wikipedia is trying to say is that the C2 error detection just points out someth

C2 is error detection, not correction. C1 is the error correction. I think what wikipedia is trying to say is that the C2 error detection just points out something is wrong, even after the C1 error correction, and so you can't fix it. But a data CD has additional error correction, so it can correct more errors.