Pauline van Vliet from Holland has written clearly about the working HHs, so-called KNPV-line dogs on her homepage 'Hollanderhuis'
Here a direct quote of her text:

"Is the Dutch Shepherd a recognized breed?

A note especially for American visitors of this web site.
The Dutch Shepherd is (in Europe, at least) a recognized pure breed just the same as the German Shepherd, the Whippet, the Golden Retriever etc. etc. As with any breed, there are also dogs not registered in the Kennel Club's Stud Book, as well as mixes of Dutch Shepherds with other dogs. A lot of the (shepherd) dogs bred by Police Dog enthusiasts are of such unregistered stock, or let us say "unofficially registered", because there is usually some record of their parentage kept by the breeder. It is mostly dogs of those lines that are imported into America. This is why some Americans wonder if there is any such thing as a purebred Dutch Shepherd. The answer is: yes, there is."

I do fully agree on Pauline's words.