In just about all the historical writings regarding to the early Tang, it is commonly said that the Tang had 6 protectorates.
They are An Bei, An Dong, An Xi, An Nan, Bei Ting, and Chan Yu.
The An Bei protectorate is created in 647 A.D. at the location of the ancient xiongnu capital(north of present day Mt. lan in inner Mongolia) to control the Tie le tribes. at the time it was not called An Bei, but Yan Ran. In 633, Yan Lan protectorate was relocated to the north of the Gobi into Han Hai du du fu in Uighur territory northwest of present day Ha Er He Lin in outer Mongolia. Its name was changed to Han Hai protectorate. Only in 669 did it change its name to An Bei protectorate. This situation lasted until 688, when the later Turkish khanate became independent and started to reincorporate the tiele tribes into their territory. The An Bei protectorate was then moved to Tong Cheng county in the Long You circuit(Gansu)
In 693, An Bei protectorate was again moved south to Xi An Cheng becaused Mo Cho khaghan raided Ling Zhou. In 708, An Bei was moved northeast to western Shou Xiang Cheng by Zhang Ren Yuan, taking advantage of the failed western expedition by Mo Cho against the Turgis. In 722, it was again moved to middle Shou Xiang Chen in present day Boutou, inner Mongolia. After 758, it changed its name to Zheng Bei protectorate.
Chan Yu protectorate was created in 650 along with Yan Ran after Che Bi khaghan was defeated, it symbolizes the subjection of all the eastern turks. There is a debate among the academic field whether in 698, Chan Yu ceased to exist and got incorporated into An Bei. Yet we do know that by 722, both An Bei and Chan Yu exist as two different protectorates.
Bei Ting protectorate was originally part of An Xi, which was created in 640 after the subjection of Gao Chang, yet in 702, Bei Ting was separated into its own protectorate and in 709 it earned the name of "great protectorate".
In 750, Tang also set up Bao Ning protectorate in Si Chuan after its war with Tubo, this was gone after the An Shi rebellion.
In general, the Tang only had 6 protectorate for at most 48 years. And possibly less. And their name and location shifts like the wind. Why does history books commonly consider the Tang to have 6 protectorates and 10 military commissions(Jie Du)? (I haven't went into the details of the military commissions because I don't have time, but they are hardly stable either).