Jin Yong's novels are long, and their huge casts of characters are typically introduced gradually through the course of the novel rather than dumped on readers en masse in the first chapter. Many characters, including significant ones, aren't introduced until late in the story. In ROCH, notoriously, two new characters (Cheung Gwun Bo and Gok Yeun the Monk) were introduced towards the end of the last chapter, and would play significant roles not in ROCH, but in its sequel, HSDS.
So, looking through the canon, who were the last new characters to be introduced in each Jin Yong novel?