Board Thread:Naruto Discussions/@comment-34277398-20180425011421/@comment-732150-20180425213756

Tobirama having created FTG in no way guarantees he knows everything about it. He also invented Edo Tensei, but both Orochimaru and Kabuto have improved on it. That's like saying that Minato can use Rasenshuriken because he created the Rasengan.