I looked it up and the official name of the country is the Republic of Cape Verde, so technically the islands wouldn't be included in the name, making it not plural.
If you're going to use St. Vincent and the Grenadines then you should also accept: Antigua and Barbuda; St. Kitts and Nevis;Trinidad and Tobago; Sao Tome and Principe, for they are also more than one..
-Honduras has two possible meanings: the depths or the anchorages; both are plural, so it can count as plural too.
Come on, you have Seychelles on the list, that comes from Jean Moreau de Séchelles (technically is not a plural).
(For those saying about Mauritius, it's named after Maurice van Nassau. Mauritius is the latin form of Maurice).