I also thought there was a good chance that C5 is Korea. It almost looks like the head wear has those dangling balls on it like in most pictures of Wang Kon. Of course, I thought B4 looked like Haile Selassie because most blurry imaged look like Haile Selassie. Come to think of it B5 and C5 look like Haile Selassie, too. Too bad Ethiopia doesn't fit alphabetically.
I'm at a loss for B5. I can only come up with Golden Horde, Ghana, or anything that begins with Great or Grand. Unless B4 or C1 are wrong, and I don't think they are, there are very few alphabetic possibilities. Ancient Ghana would be an obvious choice if anyone knew anything about its leaders. As far as I know, Ancient Ghana is a little like the Harappan or Great Zimbabwe. We just don't know enough about them to do a Civ.
Oh wait, German New Guinea... German Samoa...