This is one area where I fully expect Seabourn's move to Seattle to improve things. There simply were not enough people and an inferior reservations system so there was inconsistent pricing. With the more robust system that Holland America (and Cunard, Princess, P&O Australia) use those inconsistencies will...eventually...go away.
As Granny mentioned, she booked quite a long cruise (get ready for Granny's Adventure!!!) which when broken down into segments was less expensive. But when this was brought to Seabourn's attention it took a while for the correct pricing to be loaded into the system...and then Granny's price was actually less than the sum of the segments (as it should be).
In short, if you have a good travel agent he/she will book you under one reservation and have the pricing adjusted. If that doesn't happen, Seabourn will not require you to disembark and then embark. And, if you don't have the same suite for a back-to-back, Seabourn will even move your clothes, etc. Remember, is Seabourn...and that does make a difference.