Section on idenpotent flow says "The sequence number is implicit and is defined using a Sequence message." Suggest to add "with the explicit field NextSeqNo" to make explicit the fact that only the Sequence message itself and not the first message after it has the field "NextSeqNo". Maybe also change the next sentence to read "The first message after Sequence has the implicit sequence number NextSeqNo."
Section on idenpotent flow says "The sequence number is implicit and is defined using a Sequence message." Suggest to add "with the explicit field NextSeqNo" to make explicit the fact that only the Sequence message itself and not the first message after it has the field "NextSeqNo". Maybe also change the next sentence to read "The first message after Sequence has the implicit sequence number NextSeqNo."