I don't understand what you asked, but anyway, I think you didn't even read the post. If you're looking for addresses that match a 12 char prefix, that's one thing. If you're looking for addresses that match 1-bit prefixes, that's a separate thing. If that first bit is also the first bit for all possible hashes that have the 12 char prefix, then obviously there are more hashes that have the bit, then hashes that have the prefix. However, there are the same amount of hashes that start off with the OTHER bit, so, yes, it is possible (e.g., yes, there are existing combinations) where everything else (except your 2 addresses with the same 12-char prefix), start off with a different bit, hence not the same prefix or any sub-prefix of it (1,2... 11 chars). However, that doesn't mean that this possibility is actually found in some sequential subrange, but it is also not excluded (for secp256k1, you'd have to check all the existing 2**256 ranges that comprise of 2**66 sequential keys). And you can obviously simply create one: pick 2**66 keys with hashes starting with a 0, except two of them that have hashes starting with a 1. Oh, wait, ECC math, G is fixed, keys have an order, "it can't happen"... etc... no comment.