That's really not how it works. I draw as a hobby and I love to study human anatomy. I can conjure in my mind people in many poses with detail, in different clothes and colour. Still the act of drawing without a reference is a world in itself. If I try to sketch from memory without a reference, it quickly falls apart.
It's not that the mental image is incomplete, wrong or an illusion. Is just that knowing it and reproducing it are two very different things.