Two versions of MCCP exist. The original version ("version 1", although it wasn't called that at the time) inadvertently used a malformed option subnegotiation sequence. Version 2 corrects this, and introduces a mechanism to simultaneously handle both versions. The various client, server, and code descriptions include tags about which version of the protocol they support:
Version 2 is the better version, since it doesn't break processing of other option subnegotiation, but version 1 client support may be useful while existing servers migrate to the new version.