Board Thread:Naruto Discussions/@comment-35448581-20150520162940/@comment-2120712-20150521045220

If you ever become a manga artist then you will realize that you can not fit every piece of info into the chapters. That is why Databooks exists, to list off info that is relevant to the story but did not make it into the pages of the chapter. Could you imagine how behind we would be if Kishi tried to incorporate everyone's ninja registration numbers and all that crap into the chapters? You focus in on the story and go from there. Any other stuff that isn't a top priority can be spun off later providing your series is successful enough.

The biggest hint was when Kakashi said the Jonin level ninja have at least two elemental natures. Given that the leaf has stayed on the top of the ninja world for generations, I am not shocked that many of its shinobi have had at least basic training in many natures. The problem is that Naruto is a story where all those traditions are thrown out the window because the mc is about to bring a big political shift to the shinobi world and the fact that he is a doofus when it comes to the technical aspect of jutsu workings. If the manga focused on the Sannin's time then we may have seen how they were encouraged to learn so many natures.