Disney-comics digest #750.

[Don Rosa]

>Oops -- I forgot-- PER:
        No, there is no evidence outside of my stories that Grandma Duck is
a Coot. I knew there was that Cuthbert Coot in the family, so I saw that I
could make Cornelius an ancestor of Donald, and that was an interesting
idea. And I knew Grandma was from a farm family who seemed to have been
pioneers, so her being a granddaughter of Cornelius just seemed obvious at
that point. That also gave her a prominent spot in the "Lo$" since she could
own all of the land around Duckburg and it could have been she who sold it
all to $crooge.