These finds are the result of the archives of Van Kempen Begeer being transfered to the Dutch state/RKD. Many more finds can be expected, several items of which we think Schurmann made them, are not very well documented and if you look at the Dutch royal collection, many items are made by Dutch jewellers.
When you go to www.kb.nl/kranten and search for 'Beatrix' and 'diadeem' you will find some reports on her wedding tiara, with false information (inaugural tiara of Wilhelmina), go back further in history and you won't find any exact description of royal jewellery. It remains specialised information in which even the Queen has limited interest.
Nonetheless: there is no reason why this wonderful tiara should exist for over a century before the real maker is discovered.