Beyond a certain error rate, you will definitely end up with bad data. The point is, with error detecting or correcting codes, you're introducing redundancy by

Beyond a certain error rate, you will definitely end up with bad data. The point is, with error detecting or correcting codes, you're introducing redundancy by encoding the information into more bits than minimally required to represent that information. The simplest form is adding a parity bit, which allows you to detect (not correct) up to one bad bit. (so, say 1/8 bits or 12.5% if you store a byte of information in 9 bits) Using R-S codes you can crank up the number of bits used for encoding, which also drives up your error tolerance. Plus, in addition to detecting errors, you can even correct them. So it doesn't matter if some bits come up bad (or missing) - the redundancy is spread equally across all of the transmitted/stored bits, so it's irrelevant which bits suffer from the failure. There aren't any "old" or "new" bits.