My best bet is that the SIC seat was simply removed, as they no longer existed. I can't imagine who would have been offered it otherwise, given Jamie Wolf's obvious hatred of the Word.
While not explicitly stated, I can't imagine that the Rasalhauge Dominion has a seat on the MRBC. Given the Clan ban on hiring mercs (And the Bears' own intense hatred of them) I can't see any situation in which they would be interested in the MRBC. And besides, I've never heard of the RasDom hiring mercs either.