As for the name issue, the concept of knowing the name of your Zanpaku-to gives your Zanpaku-to more options such as compressing it's size to a more easier-to-handle state as well as evolving it to the point of Bankai.
The idea that Kenpachi doesn't even know the name of his Zanpaku-to is relevant to it's current permanently released state. By not knowing it's name, his Zanpaku-to is uncontained, unrestricted, and unleashed at it's purest to the point where it's size is ridiculously large in comparison to a regular Shinigami's Zanpaku-to. If Kenpachi had known it's name, he would have had the ability to contain it's energy in a compressed and sealed form.
Yes, in most cases, a Zanpaku-to shouldn't even be able to awaken if it's user doesn't even know it's respective name, but you're forgetting that Kenpachi -like Ichigo- is a special case with more reiatsu than normal.