A first cousin of my grandmother died in the early 1980s, an only child who left no descendants. His only heirs were first cousins-children of siblings of his mother and his father. In reviewing the estate papers some thirty years later, I realized that the family of his mother's only half-sibling had not been included. The half-sibling was deceased, never kept in contact with her family, and only living child at the time lived half a continent away. The estate was not a large one either and was overseen by a relative from the father's family who was probably unaware the long-deceased mother had a half-sister.
Court records can provide an incomplete family structure, especially if the estate is relatively small, the family is somewhat estranged, and someone unfamiliar with the entire family is an administrator.