"Embellished history," is the simple answer. "Varying degrees of embellishment, anyway. The mysticism is usually pretty spot-on when it comes to ritual, it's the," Severus makes a vague hand gesture, "running about with spears and swords bits that tend to be inaccurate. Dealings with the underworld are debatable. Most ghosts haven't experienced the whole process so they can't report back about it."