PK Sir can tell in a better manner about DHN - SLN - LKO Route in it's Historical Sense. If I am not wrong, the KOAA - JAT Exp should be the First Train to take this Grand Chord - Awadh Railway Route Combo for travel followed by Doon Express which initially used to ply via Patna Main Line - Lucknow. Then for years, there was hardly any Mail or Superfast Train until 2010 when my Favorite KOAA - ASR SF Exp was launched, being the 1st Superfast Express Train in India to join Grand Chord's Dhanbad & Gaya to Ex Awadh Railway's Lucknow .... :-)
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The...
more... Present Route between Mughalsrai & Lucknow
via Varanasi was constructed between 1887 & 1893.
Then the Present Route between Howrah & Mughalsarai
via Liluah - Dankuni - Asansol - Dhanbad - Gaya was constructed between 1906 to 1917.
This shows that trains like then Sealdah - Jammu Tawi Express & Howrah - Dehradun Doon Express started after the year 1917, thus facilitating people between Lucknow & Dhanbad/Gaya till now :-o