Brochure rate is a meaningless term. Many products use this technique, which involves publishing a high price (at which nothing is actually sold) and then offering "discounts" or allowing their dealers and agents to do it. Cars, musical instruments and many other products do this. And it is confusing to the consumer. To analyze a "2 for 1" offer (sometimes combined with partial free air, shipboard credits, included tips, and such), the consumer must first be knowledgeable as to what has been the actual "going price" for this cruise.
Sad thing is, a minority of these deals are actually GOOD, but I'm to old and lazy to do all the math required to determine this.