It might be. If it was fresh evidence and wasn't available to anyone beforehand, wasn't discoverable, and they found out after the fact, then it would be grounds for appeal.
Jaser is coming up in the Court of Appeal on the VIA Rail terrorist case. I think in the facts of that case they found out after he was convicted that he was likely unfit, and then he was found fit. A big part of that appeal is going to be dealing with what happens when a mental health thing comes out after the fact.