Exactly -- remember Dennis and Brian wrote K&R in 1978 on V6, not PWB and not V7 (or anything from Summit like TS). When Brian's typesetter independent troff was released, that updated language was needed. That was what we referred to as "typesetter C". Brian and Dennis would have put together that kit. My >>guess<< is that Mashey et al. and the Summit folks forked Dennis compiler somewhere before this time -- so what got packaged with the typesetter kit vs what got packed with Mashey and the team's kit are close but >>slightly<< different.