Re: Joker Knew of Bane's Existence.
All of this was based on Joker's belief that he could;
1. Break Gotham's people on the ferries by forcing them to blow each other up
2. Break them by destroying hope via tearing down their White Knight, Harvey Dent, and all the good work he did for Gotham
Bane wasn't even in mind when TDK's script was being written.
"Sometimes I remember it one way. Sometimes another. If I'm going to have a past, I prefer it to be multiple choice!"
- The Joker