after spending years working for a boss who has a similar npd way about him, it's amazing the similarities when it comes to lies and exaggerations. i saw with my own eyes how events transpired, and was there minutes later, when he first told someone else about it, and it wasn't that far off-base, maybe shaded a little to make himself look or feel better.
then the 2nd or 3rd time he'd tell it, he'd leave out certain details, or round up about what might be a better version of how he came off in the story. eventually, he would come up with a complete fabrication that was his favorite, and one that he thought sounded best.
then it wasn't ever about remembering the actual incident, it was about remembering the best possible version that he had told, and stiffening the details of that version to make it sound more accurate. eventually, he couldn't tell the difference anymore.
you can see when trump tries out his material, eventually, he finds a version he likes the most that he and his minions can run with. then he stiffens it to the point where it doesn't even match something he said days earlier. but he doesn't remember that, nor does he care. and neither does his 40%.