Well there are only seven instances of authority. So we'll need to decide on a final list of who the Princesses of Heart are, as those who hold the authority will be closely tied to those who are Princesses of Heart. 

I think thus far we have confirmed... 

Alice is a Princess of Heart, and the Queen of Hearts currently holds Royal Authority. 

Anastasia is a Princess of Heart, and Dowager Empress Marie holds Royal Authority. 

Lucian is a Prince of Heart, and Royal Authority is either held by his father, or it may have passed onto him when they met him on Destiny Island. 

Mickey also holds Royal Authority, but is not close to any particular Princess of Heart. (Therefor, there is room for one Princess of Heart who doesn't have any sort of figure above them to hold Royal Authority). Unless we wanted to make someone like Daisy a Princess of Heart. 

And Uther holds one more instance of Royal Authority. 

So that leaves 2 more characters that can have Royal Authority. 

Something to keep in mind is, not many people know about Royal Authority, and what it actually is, is essentially a complete mystery. That being said, it's not crazy to imagine someone like Maleficent who is sort of in the know about its existence, might try to seize it for herself, but have absolutely no way of actually knowing who has it... so she may assume any hero or leader in a given world would have it.

To put it one way, Royal Authority is not yet really central to the plot... at least, it won't be relevant until after KH1 is done. 

But like I said, someone like Maleficent wouldn't know that nobody in Tarzan's world has it. (If they don't)

Also... we can easily do what the game did, and come the end of KH1, who the Princesses of Heart are can change. Not all, but some. And with them, the Royal Authority may change as well. 

Especially if... well, I'll bring it up with Kindred.