Then it might be RPM bcoz it was the regular link for Lalbagh (now KJM P7 is the regular link) and one more thing its east for you to identify whether its RPM or LGD because most of the locos of RPM have pink band or faded red band on the side of the loco whereas its not like that in LGD. I have attached a pic you can spot the differences. Even P4s of BZA,AJJ and ED have pink band on the sides of the loco