@ others :
i) For physical counter ticket, it is hence always advisable, like in normal course, to check the tickets immediately while moving from the counter. All details - PNR No., Date of Journey, Places for travel, Train No. .. everything. For any query (including the one related to PNR No.) should be clarified at that time. Without coorect PNR No. , you are handicapped for any and all types of queries.
ii) For e-ticket, another print out is possible and hence not a big problem.