Chang'an (840) — the same event in Old Book of Tang, New Book of Tang and Zizhi Tongjian

Old Book of Tang: Emperor Wenzong died at the age of 33 at Taihe Hall in Daming Palace.; New Book of Tang: Emperor Wenzong died at the Taihe Hall…

What each source says

Old Book of Tang (Jiu Tangshu), Annals · AD 840 · 長安

Emperor Wenzong died at the age of 33 at Taihe Hall in Daming Palace.

辛巳,上崩于大明宮之太和殿,壽享三十三。
Location: 舊唐書 卷17下 開成5年 1月

New Book of Tang (Xin Tangshu), Annals · AD 840

Emperor Wenzong died at the Taihe Hall; eunuchs Qiu Shiliang and Yu Hongzhi enthroned the Prince of Ying (Wuzong).

辛巳,皇帝崩于太和殿,年三十三
Location: 新唐書 卷008 穆宗~宣宗 開成5年1月

Zizhi Tongjian (Comprehensive Mirror) · AD 840 · 長安

Emperor Wenzong dies at the Taihe Hall.

辛巳,上崩於太和殿。
Location: 資治通鑑 卷246

Place: 長安

Show on the map — open Old Book of Tang (Jiu Tangshu), Annals