There is only an 8,000 ton spread between The Princess Nine, and all were built by Fincantieri except Diamond and Sapphire, which were built in Japan by Mitsubishi Heavy Industries, who incidentally built the new turbines that were the eventual downfall of the San Onofre NGS . . . but I'm getting off topic.
Oddly enough, in spite of being built over a ten year span, the ships are pretty hard to tell apart, the only two giveaways being the additional deck of cabins on Caribbean, Crown, Emerald and Ruby, and the repositioning of Skywalker's from the "spoiler" at the very back to a lower position and a little more forward on all ships except Grand, Golden, Star and Caribbean--and they have since removed it from Grand altogether.