Why can I not pick Netherlands, Belgium or Luxembourg when buying a Select Pass?
Netherlands, Belgium and Luxembourg form 1 country for the Select Pass. This means you will receive 3 countries for the price of 1! This means that you can choose 'BeNeLux' as your country in the dropdown list when booking, if you wish to include Belgium, Netherlands or Luxembourg in your Pass.
Other bordering countries which are combined: Croatia and Slovenia count as 1 country, so do Serbia, Montenegro and Bulgaria. More about the Select Pass countries.