Basically the Stuart Diamond is part of the House Diamonds.

The tiara Queen Maxima wore for the new official portraits does not feature the Stuart Diamond.
She is wearing the tiara of the House Diamond set in it's second setting with one of the round diamonds in the centre. In the full setting this round diamond and it's equivalent are on either side of the Stuart Diamond.

The necklace and bow brooch stomacher are both part of the House Diamonds. The earrings look like the pair belonging to the birthday gift of Willem III to his 9 year old daughter Wilhelmina.