The explanation given for SeqA and SeqV is "positive, negative and zero sequence".

In part 7-3, the CDC SEQ has a data atribute (of the FC=MX) seqT, that allows as well a sequence of type "dir-quad-zero". Is this not allowed for SeqA and SeqV of LN MSQI? If yes, why do we have this attribute in 7-3; since these are the only DOs using SEQ?