Well, if you read the legaleeze or listen to the PVPs, a guaranteed cabin assignment is not "final" until you check in. That is why they don't like to give out the assignments before hand. Typically once they "close the cruise" everyone is assigned a cabin and that doesn't change. But last minute bookings at higher categories can have a ripple effect down through the TBA cabins. So to answer your question, no its not typical. Also what is not typical is knowing your cabin assignment so far in advance. Many times you won't know what they assigned you until you get to the ship!
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013