In the 1990s, with the opening of contacts across the Taiwan Strait, Liu led the way in uncovering historical materials from the mainland. Articles like "Secret Cables Between Gu Weijun and Zhang Xueliang After the Marco Polo Bridge Incident" clarified many things about the war in China.
八○年代前後，兩岸逐漸開放交流，劉紹唐又率先轉載從大陸發掘的民國史檔案史料〈九一八事變後顧維鈞與張學良往來密電〉，清楚列舉張學良與蔣中正對東北問題的異見。八七年在台出土的〈張學良進關秘錄〉，補充了史料甚少的中原大戰資料。