I think I've found why Ferdinand was not included on this Flemish jeton. The first three children of Philip the Handsome and Joanna of Castile ('Joanna the Mad') were born in Brussels, Ghent, and Leuven, respectively, in the Burgundian Netherlands. In 1502, though, the death of Joanna's brother and sisters resulted in her being the heir to the throne of Castile. She returned to Castile to be formally recognized as heir, and her fourth child, Ferdinand, was born there in Spain in 1503. On her mother's death in 1504, Joanna became queen of Castile (and Philip became king in right of his wife). Marie, the fifth child, was born in Brussels in 1505, after their return to the Low Countries. This jeton is only celebrating these four "Flemish" offspring, not the boy of Spanish birth. Perhaps, as well, because the boy was named for Joanna's father, Ferdinand, king of Aragon. When his wife, Joanna's mother, died, the rules dictated that he lost the right to the kingdom of Castile to Philip and Joanna. He became their enemy, minting coins in Castile declaring himself to be king. He ultimately succeeded in having Joanna declared insane, to rob his daughter of her right. It was after that that she became known as 'Joanna the Mad.'