LKO[officially called 'Lucknow' and colloquially as 'Lucknow Charbagh'] comes under NR. Right next to it, in a SEPARATE building lies LJN[officially called 'Lucknow Jn'] which comes under NER. They are colloquially as Badi Line for NR and Choti Line for NER[since MG trains used to originally run from here].
The issue strikes from the fact that your ticket will show the name Lucknow irrespective of the fact whether it starts from LKO or LJN. One needs to check the station code or look for the small 'jn' that affixes in case of...
more... LJN. In many cases, it has led to passengers outright missing trains and/or panicking that their train hasn't arrived yet even though on NTES it shows otherwise[In reality, the train has just arrived at the other station].
LJN bound trains previously had to undergo loco reversal and ASH was the MG terminal. With MG tracks gone, ASH is used for trains coming from GKP that take a loop via NER's tracks[there are two ways to go to Lucknow, one is direct to LKO; the other loops around a full circle; the tracks diverge at Malhaour] now. LJN is now only used for originating/terminating trains with only couple of exceptions.