Is “Historically, Xuanzang did not go to fetch scriptures by imperial order, and had no disciples.” true?

Historically (according to 《大慈恩寺三藏法师传》), Xuanzang secretly crossed the border due to the early Tang prohibition on frontier travel, journeying west alone. However, in 《西游记》 Chapter 013, he is depicted as the sworn brother of Emperor Taizong, sent on a mission to fetch scriptures, with travel documents stamped at every pass. The original text: "闻得是钦差御弟法师上西方见佛，无不恭敬。" (《西游记》第013回.txt)