I think that is a plausible possibility indeed. The other is that with the deaths of Queen Juliana and Prince Bernhard, both in 2004, the four daughters assembled together in counsel, took good advice from the plenty of the advisors the royal family has. Probably already in the handling of the two heritages, the four daughters made arrangements concerning the jewels and other properties which are "neccessary" for the kingship. After all King Willem-Alexander has the use of everything Queen Juliana already had and Queen Máxima shows us the one treasure after the other.
The strange is also that a son of one of the four Heiresses, the King, is now director of the Foundation while his mother and the three aunts are the actual heiresses of his late grandmother. It is all very complicated but so to see everything has been worked out nicely as Queen Máxima does not fail to glitter us.
It remains intriguing that only the De Bourbon de Parmes seem to show more jewels than the Van Vollenhovens and the Guillermos. Undoubtedly because they belong to a Royal House but maybe also because Margriet and Christina were somewhere compensated. The article claims that the Domain De Horsten, with 21 farms and several houses, is owned by the Queen and Princess Margriet. The other two sisters are not named. Undoubtedly there are a lot of specific arrangements. For an example the Guillermo's got more artworks, or cash and the De Bourbon de Parmes got more entrance to the jewels. Who knows? All sisters seem to go well, in great harmony, so it must have been solved with satisfaction for all.