Quoting your post from the other thread - "MAS-Beypore run dated 1868 shows Beypore train depart 5 PM, stops at every station like Passenger & so does other trains to CBE/SBC (these were no Mail which always got limited stops)"

As I said earlier, the traffic back then was too low, so the trains that carried the mail also stopped everywhere.

Attached...
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is a timetable from 1868 of the East Indian Railway from Howrah to Delhi - Notice that there are two trains running from Howrah to Delhi and both of them stop at ALL stations between Teenpahar and Delhi.

If the Beypore train cannot be considered as predecessor to Mangalore mail as it stops at all stations, and if the Bombay - Ahmedabad train from 1864 can't be considered as predecessor to the Gujarat mail, then the Howrah Delhi trains from 1868 cannot be considered as predecessors to the Kalka mail as they too stopped at all stations.

Notice that the Beypore train also skipped some stations between Madras and Jalarpet, like how the Howrah Delhi trains skipped some stations between Howrah and Teenpahar.

Also notice the train on the Allahabad - Jabalpur route. It ran in connection with the Howrah Delhi train reaching Allahabad at around 3 in the morning. It was not a separate train to Jabalpur from Howrah. It probably had through carriages from Howrah.

This same arrangement continued after the complete opening of the line from
Bombay to Howrah for many years. There was one mail train from Bombay to Jabalpur (operated by GIP railway), passengers changed to the EIR train at Jabalpur and the through carriages were attached to the train coming from Delhi at Allahabad and thus proceeded to Howrah.

You can see in the 1895 timetable I shared earlier, that there was only one mail train between Howrah and Burdwan in 1895. If the Kalka mail and Bombay mail were separate trains by then, there should have been two mails in the timetable, not one.