The Old Book of Tang indicated that Li Shiji was 75 at the time of his death, while the New Book of Tang indicated that Li Shiji was 85 at the time of his death. Compare Old Book of Tang, vol. 67 with New Book of Tang, vol. 93. The Zizhi Tongjian, while not explicitly stating that Li Shiji was 75 at the time of his death, appeared to follow the Old Book of Tang by quoting Li Shiji as stating that he was satisfied with living almost to 80. See Zizhi Tongjian, vol. 201. (The New Book of Tang, containing apparently the same quote, had a slightly different version that had Li Shiji stating that he was satisfied with living over 80.)
Old Book of Tang, vol. 67 indicates that Xu Shiji was 16 at the time he joined Zhai, but this conflicts with all other records on his birth date. While Zhai's uprising was not firmly dated in historical records, it was said to be at the end of Emperor Yang's Daye era (605–618), and if Xu Shiji was 16 in 610, it would not be at the end of the Daye era. Indeed, in 610, there would have been very few reasons for people to resist Emperor Yang's rule, as that would predate his disastrous campaigns against Goguryeo.
This account, generally now accepted, was adopted by the Zizhi Tongjian. See Zizhi Tongjian, vol. 191. However, the Old Book of Tang gave a different account: that Li Jing and Li Shiji both offered to assist Li Shimin in a coup attempt. See Old Book of Tang, vol. 64.
