I've done a similar one - http://www.jetpunk.com/user-quizzes/91108/country-borders-double-tripoints-and-4-bordering-each-other - in which I also considered Belgium-Netherlands-France-Luxembourg as wikipedia takes into account the France-Netherlands border in the Caribbean
I made a quiz quite like this, but including overseas territories 1 day later. I didn't notice until after submitting the quiz. I guess there's no need for my version any more.