Bit value to level mapping
I wouldn't mind betting that they encode the levels somewhat differently using Gray code or similar, as this would produce only a single-bit error between adjacent "levels".
i.e. for MLKC it's more probable they use the order 00 01 11 10 than 00 01 10 11 because if a voltage was supposed to be sitting at the 01 level and it instead was a bit high, 11 is only a one-bit error, 10 is a two-bit error.
Biting the hand that feeds IT
