I have booked two tickets for Mumbai to Pune in Tatkal quota. The train departs from Mumbai CST, can I board the train at Dadar station?
I don't have an official source to back this up, but when I used to travel Indian Railways from Mumbai, I boarded at Kalyan or Dadar (when my ticket said CST) and it was fine. IIRC the ticket inspector told me that after one station, they mark the passenger as a no-show and give the seat away. In any case, inspection didn't start until Dadar or Kalyan.
Disclaimer: This was over 7 years ago.
Confirmed Tatkal Tikets can't be canceled and no refund is permitted in Confirmed Tatkal Tkt. Therefore, general boarding rule can't be made applicable to confirmed Tatkal Tkt. Confirmed Tatkal berth should remain vacant for the passenger holding confirmed Tatkal Tkt.
It is based on the logic that railway can't make profits twice by selling a confirmed tatkal ticket which can't be canceled or no refund is allowed. I am not finding rule on the subject. So one has to get clarification from railway or to challenge in court.