To clarify the question - all books from the Lorien Legacies have a title that contains a number referring to one of the Garde. I.e. "The Rise of Nine" or "The Revenge of Seven".
"The Power of Six" looks the same, however in the translation that I read, the meaning of the title is changed. In there "six" refers to the six remaining living Garde and not to Number Six.
Is this a correct translation? Did the authors really make an exception for the style of the title of the second book?