MI5 is national, MI6 is international if I remember correctly, so yeah, that's probably right. The only time I've heard of 'MI9' was on this CBBC program my sister used to watch when she was younger (the evil boss had a rabbit which was like Anokata, while the 'boss' seemed more like Agasa, that program was weird). I think I'll google what Chekhov said tomorrow when I'm properly awake...
EDIT: Why wouldn't Sera delete Haibara's picture if she didn't know about the Org...?