I didn't know about dibs, but then, I am of enough distinct traditions (none anglophone except where I grew up, Los Angeles, and that a bit dicey) that convention need not come knocking. Reason uses my mother's childhood language's term for "grandmother" and my ex's mother's preferred term, which is not quite her own dad's childhood language's term but compatible thereto. (Umm, the lang of my ex's mom's dad.) Ex's mother is allergic to the idea of being called a grandparent in the clear, despite being well into her seventies--ain't no one can help her there.