Why did Ganlong call himself Huang San Ye in Ji Xiaolan with iron teeth and copper teeth? Isn't he the fourth son of Yongzheng?

I watched Ji Xiaolan with Iron Teeth and Copper Teeth four times. Ji Xiaolan was the oldest when he was the governor of Ji Xiaolan, Little Shenyang and Qianlong, so he was called Lao Ji, the governor of Little Shenyang was called He Er, and the governor of Qianlong was called Huang San Ye. But in history, these three people didn't go out together, so the title of Huang San Ye was also given to Qianlong by the novelist.