Dave, thank you for demystifying the Vision Class; I've never quite understood it. And I'm struck by the similarities with Princess' Grand Class. Grand Class is the blanket name for nine ships but it is really three sets of sisters and one hybrid. Grand Princess, Golden Princess and Star Princess started life as sisters, as did Diamond Princess and Sapphire Princess. Caribbean Princess is a one-of-a-kind; then came Crown Princess, Emerald Princess and Ruby Princess. To add to the confusion, Diamond, Sapphire, Emerald and Ruby are often (mistakenly) referred to as "Gem Class" but they are the least alike of any of the sub classes.
Ah, sweet mysteries.