What does it mean that the King of Qin in the Warring States sealed Mi Yue as a symbol?

Mi Yue became the concubine of King Huiwen of Qin, who was called Mi Bazi in history (the harem of Qin State was divided into eight grades: queen, wife, beauty, lover, Bazi, Qizi, long ambassador and little ambassador), so it can be seen that Mi Yue's original grade was not high.

Bazi was the title of concubine of the Emperor of Qin and Han Dynasties. The position is below the queen, wife, beauty and lover, and above the seven sons, long ambassadors and small ambassadors. The treatment of the Qin dynasty is equivalent to two thousand stone officials; The Western Han Dynasty was reduced to 800 stones. Biography of Han consorts: "Han Xing, because of the seal of Qin, ... concubines are all called wives, and there are also wives, beauties, lovers, eight sons, seven sons, long ambassadors and few ambassadors."