When did I mentioned 1600?
click here Hope this will resolve all your queries & it take just a little research to find information about happenings!!
Mangla was part of Big Four & it got introduced instantly after Kerala Exp got space to attach Mangla Rake as Karnataka got different slot!!
Karnataka/Tamilnadu & Telangana/Kerala Mangla slot for one way while Karnataka/Telangana & Tamilnadu/Kerala Mangla slot at other way!!