Quote Originally Posted by Sidnne View Post
It happened back when Naruto was fighting Obito, when he freed the 4 tails and learned the names of the bijuu.
http://www.mangapanda.com/naruto/572/9

Obito only put part of the 1 tail and 8 tails in Naruto, since they weren't present during that "meeting."
How did Obito know that Naruto did not have the 1 tails or 8 tails with him from before? Was it a good guess?