Earlier it was Hatia - Patna Super Express. Then, using its rake Kosi Express was introduced between Patna and Saharsa. Both trains had RSA at PNBE end. Then, Kosi Express was extended to Murliganj(if I am not wrong) and finally to Purnea Court. Later, both the trains were amalgamated to run as Hatia - Purnea Court Kosi Express.