Why do passport numbers change when renewed?
It depends weather u r passport was issued under tatkal scheme for 5 yrs or under normal scheme for 10 yrs. In case it was for 5 yrs the same booklet is used n one of the unused page is stamped as extension in validity for another 5 yrs. However if the normal mode of 10 yrs is being renewed assuming u r passport is nearing expiry then the PSK will stamp the old passport as cancelled n a new booklet will arrive thru registered post on a later date after police verification