Got some interesting answers by google search:
1.

Vinod Vadakkadath, In a constant state of crisis
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of all, reservation is a fairly recent process, introduced only sometime during the 1970s. And until the system was computerized, simply put, you could not do any booking across cities/towns. At a station you could book only on trains that passed through there, and the number of trains for which reservation was available was very less also. The "from anywhere to anywhere from any station on any train" booking system originated only with computerization of the entire system.
Before that, each station was allotted a definite number of seats in every train. (quota). Each entry would be made by hand in a register by a reservation clerk. And the ticket would be handed to you (yes, the small card-type tickets). If you made a cancellation, your entry would be struck off the register. Reservations could be made one month in advance (I think) and each day a new page would be opened in the register for reservations starting on that day. Waiting List movement was just as it is now. At a specified time before the train departed, the list from each station would be sent to the starting station by telegraph where they would compile everything and do charting. So, it was basically the same system today, only that everything was done manual and by hand.
Later, another system emerged where you could telegraph/send by letter your booking requests to station masters of faraway stations and send the cost of the ticket by Money Order. They would book the ticket for you and send you the ticket by post. Of course, this was fraught with dangers. And Station Masters and TTEs controlled almost the entire booking process and who got what ticket.
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2.
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Jitendra Bhavsar, Dad served Indian Railways for 38.4 yrs
I will give some reflections from my memory

a. Trains halting at station

Each station had a register (railway book and not the college type register) and that book at several middles pages was folded with various train numbers written largely that halted at that station. A passenger desiring a reservation in a train that halted at that station would request the booking clerk who would then grab that register and open the desired train page. The passenger would ask berth(s) for a particular date and the clerk would check the register if the seats/berths were available. This clearly indicates each halt had a quota. If available, a general card ticket for the journey was taken by the clerk. The name, age, sex of passenger with date of journey was written in register. The coach and berth number would then go on the card ticket with the total fare written (sometimes).
If there were no card tickets, then a paper ticket was prepared by the booking clerk with passenger name, total fare and coach details. Coach is quite a modern word here in this note. Those days "bogie" was very commonly used term.


b. Trains not halting at station

Passengers could ask for reservations from other stations. The booking clerk would take a passenger request and the request used to get forwarded to the station where the train halted using a railway telegram. A confirmed message arrived by the telegram to the station again. The passenger would make a second trip to see the status. Return journey reservations were also booked in similar manner.
Remember that communications is one of the best mechanism that the Indian railways had even in those days. The other mechanism is the meticulous planning and detailed procedures that were laid down from time to time.

Vinod's answer is also perfect. New page for each date was valid for stations which had a larger quota, which was quote rare. Eg. Jalgaon station a district place in Maharashtra had only 2 berth quota on the 1Dn Calcutta Mail via Nagpur. My Dad worked both at Jalgaon station and Pachora Station where many trains had only 1 or 2 berth quota.

Note: I am a son of retired Mail Express guard from Indian railways. Before coming to the Operating department, my father was in Commercial department and he was a booking clerk from 1963 to 1981 (also a parcel clerk in between) on a small town station in Central Railways. I have several memories of this register based reservation done by my Dad when I went to deliver his lunch with my grandmother. I got Re 1 every day on return from my Dad for which my grandmother used to purchase a milk sweet "kalakand" while returning home.