Among the development notes, mostly consisting of rough sketches and storyboards, are some preliminary plot notes with some ideas that were never used in the game. One such plot note covers details about meeting the character Yuffie Kisaragi. The following is a translation of the plot notes:
(Prep) From the opening and forward, wanted posters for Yuffie can be seen in town here and there.
Yuffie is a fugitive. Her age and what she looks like is different for each poster.
(How to make her join)
Or, she will attack Cloud when he is sleeping in an inn.
Either event can happen anywhere.
From this point, Yuffie can be recruited at any time.
The Wutai event requires Yuffie and therefore, she must be recruited in order to complete the Wutai event.
What Yuffie looks like (and her level) is determined when she first joins.
(This is based on the last wanted poster that was viewed)
Therefore, by selectively choosing which wanted poster you look at last, you can recruit the Yuffie that suits your liking.
Sadly, there were no rough sketches for the different Yuffie styles (Or anything on the potential resurrection of Aerith for that matter). Still, it's an interesting look at some of the ideas that went into the game and what might have been.