Henri - I notice in your calculations that you are using the grandparents, and not the parents. Of course that plays a factor, but you must first factor in the parents, then the grandparents. Thus - I believe that your calculations might need a bit of reworking. Correct me if I am wrong, but I do not believe that I am. If Queen Wilhelmina - as your furthest relative, is 50% German, 25% Russian, and 25% Dutch, and her husband German, by rights that made Queen Juliana indeed 75% German, 12.5% Russian, and 12.5% Dutch. Then it would stand to reason that Beatrix would be nearly 90% German, and 10% other. However, given that this is all regarding the blood line and not the actual citizenship, then I think that it is a moot point. However, in any case Catharina Amalia would be 50% Argentinian, and basically 50% german.
But since we all know that she is 100% Dutch for everyone who cares, I think that the Argentinian/German influence is somewhat minimal. She also looks 100% Dutch, but there you go.
I think that the first calculation on bloodlines first goes to the parents and only then to the grandparents, ad infinitum.