Meaning, can you take INA multiple times towards the same Natural Attack? So claws 1d6 to 1d8 then 1d8 to 2d6?
No. It doesn't say it can be taken multiple times, so it can't.
Of course, IMO it should say the that you could take it multiple times, but for different attacks each time. I've certainly seen enough statblocks where INA has been taken for several different attack forms in official adventures.
(At least in 3.5 adventures, where that text did exist. Maybe Pathfinder specifically changed it so only one attack can possibly benefit from the feat)
In any case, a specific attack form can only benefit from the feat once.