Li Yan
In Qing Dynasty, a scholar named Shen Bingzhen(沈炳震) cited some sentences from "New Book of Tang" that doubted whether Li Yan was the 19th son of Chengmei. In the opinion of New Book, Chengmei was too young to have 19 sons; Li Yan was created Prince of Xuancheng(宣城郡王) only one year after Chengmei was created Prince of Chen. "Old Book of Tang" referred Li Yan as "the 19th son of Prince of Chen", so Shen thought "Prince of Chen" here referred to the former prince Li Gui(李珪), the 19th son of Emperor Xuanzong of Tang, thus Li Yan was indeed the 19th son of Li Gui. However, in the view of Shen, this was also under doubt, for it was too late for a grandson of Xuanzong to be created a prince.