It mentions 5 Kenpachis (including the current one). It looks like the 7th was Kyouraku's friend and looks like Ginjou. He might be Ginjou's father, plus his zan had soul sucking abilities. The only reason he lost to the 8th Kenpachi, was because he was forbidden from using his bankai, since he would obliterate everything a few times the area of SS, including those that witnessed the fight. He declined the proposition to join Squad Zero.
In the novel, Zaraki faces the 8th Kenpachi, that was imprisoned for some reason until now. Squad Zero was supposedly send to hunt him down, but he was owned by Kenpachi's Kendo Slash before they appeared. Looks like as long as it hits, it defeats anyone. The Fake Bach might have been fighting him at long range taking advantage of Kenpachi's close range style.