Revealing mistake: In the opening sequence, as Nameless is entering the Emperor's palace, you can easily see in the close up shots that the crowd of black-clad people on each side is at best three rows deep. However, shortly before he actually reaches the far side of the inner courtyard, the camera pans back to reveal thousands of people, filling the courtyard from one side to another. (00:03:05 - 00:04:25)
Revealing mistake: In the final fight scene in the desert between Broken Sword and Flying Snow, when the camera cuts to the wide shots of them standing there, looking at each other, you can see tire tracks in the sand. (01:24:30)
Answer: It was a fiction based on the true historical period as backdrop, althought it sorted of resembled a true event that the deserter general of Qin gave his head to an assassin as a pass to get close to the Emperor, who was then still a king of a state among the warring states.