Nika isnt a late edition to the series
We know that NIka hasnt appeared for 800 years.
The DF has a book catelog. In those period, someone must have recorded the fruit as a normal fruit, which is what lucky roux used to describe the fruit. Since the DF hasnt awaken during those period, it would look like a normal fruit according to the people that recorded DF powers.
In this page, lucky roux clearly shows how they got the fruit and that he is using a book that has a picture of the fruit.
Shanks explaining the fruit again.
Luffy here is eating the fruit, as if the fruit wanted him for some reason.
You have to remember that shanks should have gotten the df fruit from somewhere. In the picture above, lucky roux highlights that they have stolen the fruit from an enemy. That enemy turned out to be Who Who, who was guarding the fruit.
In reality, Nika was never a retcon. The reveal in wano closed the question as to where shanks got the fruit in the first place. No one knew how to get DF from others, otherwise the WG would have had those DF to themselves. Which explains why shanks couldnt get the DF from luffy.
Keep in mind that only BB knows the method to extract DF from people.
