Some theory thoughts --
No one should ever, ever, ever claim their role (prior to mission 5). This is specifically referring to the Lancelots, since Merlin and Percival would never claim. Don't claim. Just don't do it. Don't use it as an example of "Yeah, you were right with your read earlier, but now I'm good!" This gives scum a 50/50 shot of winning even if three missions are passed.
Also, don't try to deduce other's roles in thread. Keep in mind, you have different information than what Modred has -- but he still has a decent amount, and will be able to read into our thoughts. Saying "I think player X is Good Lancelot!" gives away a lot of information, and if you're trying to fool Modred, chances are you are going to fool your teammates more. I don't think there should be anything more than good/bad. People trying to fit someone else in as Lancelot gives away the fact that they're not Lancelot -- I think we should avoid this.
One thing -- I think if we get to mission 5, and Evil Lancelot is now good, he should absolutely claim. Mordred already knows who he is, so he's not narrowing down the Merlin pool anymore by claiming.