Good point. However Kishi as a writer is not going according to his original plot,(If he ever had one). He's changing the storyline either to suit consumer demands or to extend the series even further than he planned. Thats what we're saying. Every story naturally has loops. He goes back for the loops and attaches strings to them, linking them to the present. He could back to a point in the chuunin exam, and say the barrier created by Oro's thugs during the 3rd Hokage's and Oro's fight was a Dragon Sage mode technique or a copy of it, and he'll provide enough evidence to prove it, and we'll believe it
Are you an author? I'm asking because I think it takes another author to realize and comprehend this concept. I've written some works myself, though I've never published or even attempted to publish them, but I know exactly what you're talking about, its what authors do actually when they need to advance the plot. Most people don't understand this though, that an author can create a back story out of nowhere from anything that has already happened and simply link it to some new idea they just recently came up with so that there are no plotholes. Or simply cover up a plot hole by creating a backstory.
I agree about the dragon sage thing, it is plain and simply made up, there was np foreshadowing of this, its something that Kishi recently cooked up. Surely we aren't expected to believe that Juugo, Sasuke, Tayuya, Kidomaru, Kimimaro, Jirobo, Sakon, and Ukon were all using nature chakra without even knowing it, that's bull, someone would obviously realise when an external source of chakra was entering their system.
What also doesn't make sense is how Orochimaru was unable to find that cave, shouldn't the great snake sage be in the land of his snake summons? In that case a simple reverse summoning would get him there, why was that so hard to do. Or does kishi simply want an excuse for Oro not to have known sage mode.
Also, in part one the cursed seal was explained completely differently to what Kabuto said, there are so many things about its mechanics that were revealed back then that are contradictory to what Kabuto has said, Kishi really needs to brush up on this one, its not so much that Kabuto has a power up from the snake clan that is the problem, that was pretty much expected, but I think the way he introduced it was very flawed and lame.