A centuries-old custom was for parents to give the same first name to more than one of their children. In such cases, the children were either called by a shortened version of their name, or went by their second name. This custom seems more prevalant in cases where a child died at a very young age.

The case of Cornelis Wilhelmus is a prime example. He was called Willem. His older brother, Cornelis Albertus, was called Kees, and his next younger brother, Cornelis Adrianus, was called Arie. Then to add to this story, Willem had a younger sister, Cornelia, who was called Kee.