Lying is part of the disease of alcoholism. I don't bother trying to figure it out anymore nor do I fret over the lies because I have come to expect them. Basically, it's turned to a point where I don't believe much of anything he says....ever. That's just the nature of the alcoholic dance. If I step away from the alcoholic, I don't have to validate the lies or invalidate them because it just starts to not even matter.
And, the other thing I realized over time is that if I know the truth, then why do I want him to face up to it or to throw it in his face? To shame him, humiliate him, etc? He does that enough to himself as it is. I can just let him be and let the lies go because I have finally accepted that that is who he is and it's part of what alcoholism does within him. For me, the answer came with acceptance and it has brought me more peace.