No, you just have to read the first 3 bits, if the corruption is in those. But yeah, you can't detect a single-bit corruption if you haven't actually read that bit.
You can't detect single bit corruption of the encoding without reading that bit. But what you care about is whether the encoding is sufficiently corrupted that you can't decode the original.
What if the corruption is in the last bit? Do you somehow magically know it's not in the first 3 without reading them?
In this formulation I believe the last bit would also be repeated 3 times, and you’d have to read those three bits to detect corruption.
Yes but how would you know that without reading all 6 bits first?
You wouldn't, as long as the bits are received sequentially. I think the idea is that, depending on where the corruption is, you only need to read up to two bits past the corrupted one