Unless you are cruise air , you can't join the ship at Key West (Jones Act) .
If you flew on to the next port if it was anywhere in the Caribbean , you probably can join the cruise . Other wise no go about Key west.
The same thing applies to 7 & 14 day cruises from Seattle to Alaska .
SS Ithaca , Volendam , Mariner of the Seas (x2) , Veendam , Coral Princess , Island Princess (x3) , Emerald Princess,Sapphire Sapphire (x3),Diamond Princess