SPOILERS GUYS, THIS IS ABOUT KH2:
Sora's situation is child's play. What about we had an Ansem but it was actually his Heartless? Then it wasn't his Heartless but Xehanort's Heartless who posed as Ansem for a while and thought it was a good idea to jump into the darkness with his merry friends and divided into a Nobody, Xemnas (anagram of Ansem with a X), and the Heartless that people thought was Ansem. Throw DiZ into the mix, who's actually the real Ansem and had kickass Christopher Lee voice in English. Now in BbS we have Terra and Master Xehanort and both have physical characteristics of the Xehanort the real Ansem meets before KH1 happens.
lulz!