I'm a little confused, what point are you trying to make?
I don't know why something needing to be "unlocked" matters, but you need to defeat the original members and have maxed abilities in order to get to CoR and fight the corresponding member. This also includes finding the absent silhouettes. Still, not sure why this matters since all of the data battles were secret bosses and had tweaked/new abilities, along with the absent silhouettes including Vexen, Lexaeus, Zexion, Marluxia, and Larxene. Plus, KH2FM introduced a new, forced battle (Roxas), which is something I'm unsure has been done before. BBS might do that assuming you fight Eraqus' new armor, even though that'd be more of an "added form" than an entirely new boss battle.