Chuckles,
it's actually even somewhat more complicated as RCI says on its web site:
The "Vision"-class is actually made up of three pairs of sister ships: "Splendour of the Seas" and "Legend of the Seas", "Vision of the Seas" and "Rhapsody of the Seas", and "Enchantment of the Seas" and "Grandeur of the Seas". Add to that that "Enchantment of the Seas" was lengthened some years ago, so she is also no longer a true sister to "Grandeur of the Seas", as well.
Also, there are quite a few differences between the first three "Voyager"-class vessels and the final two, as explainted on
this very nice web site.