We called both Grandmothers Nan, and called greatgrandparents Gran.
Grandfathers were called Grandad, Great grandads Grandpa.
Maternal set were Scots , Paternal set southern England.
DS called both grandmothers Nan (Nanny when small), both Grandfathers Grandad.
DGD calls both myself and her Maternal Grandmother Nan.
She calls her Great Grandmother Gran, and her great great Grandmother Grandma.
Great grandfather is Grandpa, she hasnt got a great great grandfather.
To tell the difference she just adds the grandparents name.
We came from a middle class Jewish family , on Paternal side, and a working class Free Kirk Family on the other side.
Paternal Grandmother had aspperations as well, but still prefered Nan.
I would hate to be called Gran.