On our return from Ljublana in October (award tickets), we discovered that NW had not properly reissued the ticket after the latest schedule changes. We were able to check in & fly LJU-PRG-AMS on Czech Air, but the actual tickets still showed a now non-existent flight for AMS-MSP. The reissue was handled by the KLM transfer desk in AMS.

In this situation it is possible to see the correct flights on-line even though your tickets are for different flights.

When there are changes requiring tickets reissues, its a good idea to keep an eye on the ticketing history and be sure they're done before you leave.