The 'cheaper by the dozen book extra story' is special because it can delve deeper into the family's values. It may show how they uphold certain traditions or create new ones in the face of different situations. Also, the way it portrays the family's unity in difficult times, like when they face financial problems or community issues, is really remarkable and makes it a unique addition to the 'cheaper by the dozen' series.
It's special because it can explore new aspects of the family's life. It might introduce new characters or expand on the relationships between the existing ones. For instance, it could show a closer bond forming between two siblings who didn't interact much in the main story. This expansion of the story world is what makes it stand out.