You can argue that, but instability is not multiple personalities to my mind. I'm not up to date with Batman continuity but when Johns first put forward the idea of there being Three Jokers my assumption was that he would point to the original Golden-Age criminal (as he has), the classic Joker of the Silver and Bronze-Age, and the modern deranged 'SAW' maniac who is addicted to sadism and body horror - Three quite different and distinctive interpretations of The Joker.
Instead of that though we get this odd statement from Geoff Johns as to who is what. Why it is Johns sees the classic "Clown" Version and the "Comedian" of The Killing Joke as two seperate Joker's is bizarre... I really don't know what he is thinking to come to this conclusion while omitting the clear differences with the modern film-influenced 'torture-porn' version of the character. This one really is a different man to any version we have seen before now.
But really my point is there was no need for this story. As interesting a tease as there being Three Jokers in action was the reality of it didn't make sense. Why does this toxin apparently create clones of the Joker, all criminal masterminds, all insane in the same way, and all acting the same way? It makes no sense. How on earth is it that Batman apparently deduced the Joker real name not one week after first meeting him but never noted that there were three versions subsequently running around?! Is that even possible, that THREE version of the Joker have been in action for virtually the Batman's entire career, and no one picked up on it?!
This series wasn't exactly terrible, but it doesn't bear up to much inspection either....
So the true Joker would be the classic silver age one then?