Not sure about the ins and outs but Shihan is a title as far as I know. Theoretically it only works within an organization but even that's fuzzy.
What I mean is I would not necessarily address Chiba sensei as Shihan but would definately address Nariyama Shihan as such. By fuzzy I mean that in a face to face confrontation or letter I would probably use Shihan to both - in fact my last letter to an Aikikai Shihan I did just that. Peter G. please tell me if I'm making a fool of myself.
Sensei itself is funny - at what point do you address people that are not teaching you directly as sensei. It's a lovely balance between age, experience, culture and familiarity - but that's topic for another poll.