The first question about the stadholders will always be: 'What is a stadholder?' Originally the stadholder was a kind of governor of a Dutch province. This was also the title by which they were often called when the Dutch wrote in French about their 'gouverneur'. Governor is however a very strange name for a dignitary that had noone above him. It's therefore understandable that the Dutch term 'Goeverneur' is never used for a stadhouder.
Of course some of the Dutch provincial states considered themselves to be above the stadholder and him only to be the first servant of the state. However, this could have very little meaning when the stadholder had to appoint them to their offices, as was the case in Gelderland and Overijssel. The Stadholder's power also varied from province to province and in some of them had a solid foundation on feudal rights. Add to this the fact that he was a prince in his own right and inherited the function and one has a recipee for confusion.