I think they do know, if they stopped to really think about it, which they don't. They lie constantly, constantly framing (and then reframing as necessary) their image and backstory, lying is nature to them and I don't think they spend much time thinking about whether what they are saying is truth.I'm really interested in all this too, and I've also long wondered - do they know when they are lying? Or do they legitimately believe they are telling the truth, even when they spout the most obvious of falsehoods?
ETA good morning everyone!
The reason I think they do know that they lie is that I've seen the lengths they will go to to keep a lie covered, and how they behave when they feel a threat of being exposed. If they had total confidence in their stories, so believed their lies, they would not feel threatened as there would be nothing to uncover, nothing to hide.