Correct use of adjectival forms for countries

The official name of the country is The Kingdom of the Netherlands.

Its government has recently been making an effort to have people around the world use Netherlands rather than Holland - which is the name of two of its provinces "North Holland" and "South Holland".

They aim to reinforce this idea at both the Eurovision Song Contest - to be held in Rotterdam this year, and at the Olympic Games.

However there appears to be no effort to move away from the adjectival "Dutch", which is the word that most Dutch people themselves use, when speaking English.

This latter always seems a little surprising to me, since until as recently as the mid-nineteenth century the word (in English) included both German and Dutch. (And one thing the Dutch are likely to be offended about, is being merged in anyone's thinking, in any way with Germany.) Indeed in the US, Pennsylvania Dutch, is a dialect not based on Dutch but German. It could be that some Dutch people are sensitive to this and hence those such as your supervisor speaks of "Netherlands windmills".

If I were you I would be guided by your supervisor's use - the person is after all Dutch (or a Netherlander*).

*If you call them "Netherlanders", they are unlikely to be offended, though they may look at you a littler strangely, as Scots might if you called them "Scotlanders"!