Chang'an (626) — the same event in Old Book of Tang and New Book of Tang

Old Book of Tang: Li Shimin ascended the throne at Xiandian Hall in the Eastern Palace in Chang'an.; New Book of Tang: Crown Prince Shimin ascended…

What each source says

Old Book of Tang (Jiu Tangshu), Annals · AD 626 · 長安

Li Shimin ascended the throne at Xiandian Hall in the Eastern Palace in Chang'an.

八月癸亥，高祖傳位於皇太子，太宗即位於東宮顯德殿。
Location: 舊唐書 卷2 武德9年 8月

New Book of Tang (Xin Tangshu), Annals · AD 626

Crown Prince Shimin ascended the throne as Emperor Taizong.

甲子，皇太子即皇帝位
Location: 新唐書 卷001 高祖 武德9年8月

Place: 長安

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