Passenger Name Record (PNR) number is a pointer to a record in the railways database. The PNR record contains multiple subtle elements.
The PNR number itself doesn’t store any information about the person. Rather, it focuses on a one of a kind record in the main database, which really holds all the data of the trip. See here:
Initial 3 Digits
They let us know from which PRS the ticket has been reserved.
The PNR Numbers’ beginning digit does not rely on upon the PRS from which it has been reserved.
It really relies on: Zone of the Train, w.r.t. beginning station of the train.
2,3: NR, NCR, NWR, NER
4,5: SR, SWR, SCR
6,7: NFR, ECR, ER, ECoR, SER, SECR
8,9: CR, WCR, WR
e.g. In the event that a ticket is reserved in Rajdhani Express (Mumbai to New Delhi), as the beginning station is Mumbai, PNR will begin from 8.
The ensuing 2 digits detail particular PRS.
Last 7 Digits
They are arbitrarily produced numbers. They represent no data.
PNR number exists for least 9 month as the TDR recorded can last at most 9 months. It is then flushed out. (Typically)
Following a year, the same PNR number can be produced.