One of the most challenging aspects of grandiose thinking in narcissists is that, in hindsight, you are certain nearly everything was a lie. Like the boy who cried wolf, you no longer believe anything he/she has to say.
As stated at the beginning, it is hard to call their bluff, so you never get the true satisfaction of "catching" them. They either blow up into a rage, cut you off entirely to avoid having to prove anything, divert attention on to you and how "delusional" you are for doubting them. The only thing you can count on 100% is that you will never be given proof.
Narcissists have troubled relationships. They limit themselves to those who "worship" them but if they stop supplying the ego, they are discarded without thinking twice. My theory is that, though lies are hard to prove, over time most people just start recognizing their tales are impossible and just go away.
A narcissist rarely makes a mistake - and they will always find a way out when challenged with the request for proof. But my ex made one slip up that my parents never told me about until we had separated. That is the one example I will share out of a lifetime of lies.
We were moving to Phoenix and he went first, having obtained a job. He stopped at a restaurant between Illinois and Arizona, where they had a contest if you could eat some gigantic steak, you would get it for free, get a photo on the wall and plaque, etc. Never thinking my parents, after helping me move, would stop there for fun to admire his accomplishment on their return trip home, they were amazed to find they had never heard of him, there was no photo, no nothing.
He was simply making conversation, making things up, to be the center of attention one evening...so invented this tale. That is what happens - needing to constantly be admired and the center of attention, they create stories. This was the only time my ex "slipped up."