Actually, that is a Cookeville. There were multiple family members that worked at the store where the Mackie brothers bought most of their comics. Their names are lost to the ravages of time, but there were two sisters that worked at the family store, one whose first name started with “S” and the other with “N.” Just speculation on my part, but earlier copies mostly had SN and later in the collection the NN was seen more. Maybe NN was a younger sister that worked in the store as she got a bit older.
I really wish CGC would correct the write up about the collection. The two sisters were not the Mackie’s sisters. If they were, the initials would be SM and not SN. And if your family owned the store, why would you be buying comics from your own store?