LKO and LJN are part of the same building complex.
The original Lucknow station in the 1800s was a pure BG station. When MG first came to LKO, it had a single platform near the present-day Parcel office.
I...
more... have posted earlier about the layout of Lucknow station in 1917:
/blog/post/3661564In the 1920s, Charbagh station was constructed and it still had just one MG platform.
In 1949, due to increasing traffic after independence, the OTR (the company that owned the railway) decided to expand the MG portion of the station.
In 1954, a separate complex was constructed at the north-west corner of Charbagh station for the MG lines. This is the LJN station of today.
Both LKO and LJN were called 'Lucknow Junction' for a long time. Even now, RBS lists LKO and LKN as 'Lucknow Junction' only. 'Lucknow Charbagh' seems to be a recent change.