This confusion exist as long as geocaching.com works on the country iindication placed by the CO's and Project-GC works with a combi of country(CO) and polygons.
In geocaching.com there are different country names for the same area
Netherlands Antilles, Curacao, Boniare, Sintt.Marin, Saba , Sint Eustatius, Aruba are counrtries at GC but infact before 30 september 2009 the Netherlands Antilles was a country consisting of 6 islands.
After that date the Netherland Antilles was dissolved and Curacao, Aruba and Sint Maarten becane autonom countries inside the Kingdom of the Netherlands and Bonaire, Sabe and Sint Eustatius special regions inside the Kingdom.
Hense the confussion , some CO's still use the old name and others are using the islands name.
There is still an added complecation that the country Sint Maarten does not exist in GC therefor CO's are using two names Sint Martin or Netherlands Antilles.
If you use the map compare to get all the active caches it is necessary to use the Centre/radius in stead of the country location.
By the way this is also the case when Nevis and St.Kitts because GC uses 3 different country names for the islands (Nevis and St Kitts, Saint Kitts and Nevis and St Kitts)