All of ours have different names. My children's great-grandparents are still talked about, even though only 1 is alive, and they don't really know him (he lives far away and is too old to travel). He is Papa. The others were Mimi, Nana, and Granddaddy.
My children reused Granddaddy for my father (we called his daddy "GD"). They differentiate by saying "your Granddaddy" and "our Granddaddy".
My own great-grandparents were very young, and they didn't die until I was 30. I called them Mamama and Pappa. Which was dfferent than my grandparent names.
We're obviously from the deep south. I can't imagine calling them all Grandma Faye and Grandma Gloria. Seems weird to me. LOL cause, honestly, PawPaw is a little odd. LOL