If someone sues me for defamation and I'm spoken guilty.
And when I might even have been prisoned for it, if this would change something, and after my punishment past it is figgured out that I was right. 

Would this afterwards change something?

Would it be still defamation if I asumed I'm defamating the person but unkowingly told the truth?


And in both cases: Would I be able to sue that person for defamation?
As the person knowingly defamated my reputation by suing me for performing defamation.