1st you have to have a cruise guarantee!!! By booking early that does allow you to get better upgrades. they are more likely to sell a 4a guarantee over and over again than a higher category. so they will upgrade the 1st people to book in the 4a so they can sell that cabin again!!!
it just like the airline tickets. you could be sitting next to someone on the airline that paid 250.00 for their ticket when you paid 500.00. same with cruise cabins you could have paid 599.00 when your neighbor may have paid 399.00 for the same category/cabin/deck etc. Normally the cruise rates start out a little higher. If that ship is not selling they will drop that prices and upgrade the already booked passengers!!! i hope i am not confusing you! I know what i want to say but sometimes writing it is harder than explaining it!!!