When was Huangdi Neijing lost?

I don't know, because it is not recorded in Historical Records, but Sima Qian recorded the biographies of the Five Emperors according to folklore, and the existence of Huangdi Neijing is speculated according to the modern Huangdi Neijing, because Huangdi Neijing is named internally. In addition, it is worth mentioning that The Four Classics of the Yellow Emperor was unearthed in 1973 in Changsha, Hunan. What is certain is that it is the first book of Xuanyuan Huangdi, and its content is mainly a summary of the experience of monarch rule, which can also be said to be a book on the path of monks. 1980, The Wei Yan of Waijing, discovered in Tianjin, is also a book based on the theory of Neijing, which expounds the theory of meridians and six qi in Neijing, with a total of nine volumes and nine articles.