NWR of 1943 is now PR.
Legend:-
1. Royal Blue Dotted Line -- Track Re-Laying going on.
2. Turquoise/Light Blue Dotted Line -- Gauge Conversion going on.
3. Rivers are marked in Light...
more...

Blue Colour.
4. Red Line -- New Railway Projects of PR going on.
5. Blue || Line -- New Projects Planned.
6. Green Dotted Line -- Projects went wrong.

Janta express trains were introduced after independence. There were no Janta express trains before independence.
And regarding the 'proof' I provided, You mentioned a 'pre-independence' train and I provided a 'pre-independence' timetable. I guess there is no need to dismiss it as irrelevant.
There was a 'Delhi' express that ran from Colaba terminus to Delhi (Short terminated at BCT from 1930), which started in 1911. You can this in the timetable from 1937 - click here . At the time, the Frontier...
more...

mail and the Delhi express trains were the only trains to Delhi operated by BB&CIR. From December 30th, 1945, it was extended to Lahore via Bhatinda and renamed as the 'Lahore' express. It was this train that was restarted as the FZR Janata express - click here . Also, after independence, the train was restarted as 23/24 BCT-Delhi express (It was running between these two stations in 1961). Only later was it extended to FZR.
Before the Frontier mail in 1928, there were no regular trains from BB&CIR to Lahore or Peshawar. The only trains between Bombay and Lahore were the GIP Peshawar express (Also known as the Punjab mail - present day 11057) going via Ambala, Amritsar and the GIP Punjab mail going via Bhatinda, FZR, Kasur. BB&CI only operated postal specials between Bombay and Delhi, which connected with the GIPR trains at Delhi. Their main route to Lahore was Bombay-Ahmedabad by BG, Ahmedabad-Hyderabad (Pakistan) by MG, and further to Lahore by BG.
The Frontier mail in 1928, was the first 'regular' BG train operated between Bombay and Lahore by the BB&CIR. The Frontier mail did take the route via Bhatinda initially, but it was diverted via Ambala,Amritsar from September 1st, 1930.
Many trains did go between Delhi and Lahore by the route you mentioned, but none of them were named as 'Punjab express'. And 19023's predecessor definitely did not run between Bombay and Lahore between 1912-1937. The extension to Lahore only came shortly before independence and the train ran to Lahore for barely over a year.

I was talking about the 'Punjab express', which is the precursor of the present day Doon express between Howrah and Dehradun. Earlier it was going till Lahore via the LKO-MB-ASR route, with through coaches to Dehradun. This was the only train with the name 'Punjab express'. This was a different train from the Calcutta Punjab mail.
The 'Punjab mail' is actually a very confusing name. Pre-independence, most of the trains bound to Delhi and beyond from Calcutta and Bombay were referred to as Punjab mails.
...
more...

Present day Kalka mail was a mail train from Calcutta to Delhi, with through coaches continuing on to Kalka and Peshawar by separate trains. Before 1933, it was also called 'Punjab mail'. It used to go via the main-line (Patna) between HWH-MGS. It ran with the numbers 1/2.
At the time, there was another 'Punjab mail' belonging to the Oudh and Rohilkund railway running between MGS and Peshawar with the numbers 5/6. From October 1st, 1933, the MGS-Peshawar mail was extended to Howrah via Patna, and the existing 'Punjab mail' from Howrah was re-routed via the Grand-chord (but it still had through coaches connecting to the Bombay Punjab mail at Delhi). Thus, from 1933, the 5/6 became the Calcutta Punjab mail, while the 1/2 became the Calcutta Delhi mail. With Calcutta getting a separate train to Peshawar, the 1/2 gradually started taking more coaches to Kalka and eventually became the Kalka mail. The 5/6 is the present day HWH-ASR mail.