Dwayne- That sounds correct. I can't see the cruise ship making you take your luggage off even if you have different cabins. But, I also would do a B2B unless I could book the same cabin for both. If you have to get off the ship for customs, then you probably only need to bring your passports and declarations card. I assume that they could check you in at the Pursers desk for the second leg? Or maybe they service the B2B folks first so you don't have to wait in line.
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
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013