The question has to do with the number of birthday parties the family has celebrated. Adding up the ages only works for the kids and grandkids. With JB, Michelle, Grandma, and spouses, you have to add up only the years since they married. 33 years apiece for JB and Michelle, 9 for Anna, 2 or 3 for Ben and Derick, etc. This current family didn't celebrate Grandma's birthdays when she was a child, for example. Perhaps add Amy (didn't one of her birthday parties take place at the Duggar house).