Hi David,
Some of the cruise ships which have been lengthened, which quickly come to mind:
The Royal Viking trio built in Helsinki in the 1970's (including also Black Watch and Boudicca), lengthened already in the 1980's, the third sister is the ALBATROS.
others:
COSTA EUROPA
ENCHANTMENT OF THE SEAS
NORWEGIAN DREAM
By the way, the mid-section for Norwegian Crown/Balmoral arrived at Blohm+Voss a couple of days ago and the ship is expected there on November 15.
Kind rgds,
Aleksi