[userbinator]

At least which schemes like Reed-Solomon, the "ECC bits" conceptually are not a separate piece of data that is computed and then added to the data to be protected, despite that being how it is usually implemented. The algorithm really "expands" the data, so the redundancy is spread out across all the bits. Thus any bit errors anywhere in the whole encoded "codeword" can be corrected, up to the limits of the code.