And how exactly does it cut that? There is really no doubt anymore that the "D" is connected to the Void Century. The only thing missing is an 'official' confirmation of that, which is nothing more than a formality at this point. The Void Century was 800 years ago and you only need two generations of a family to potentially create a new family and here 8 centuries passed...you could have easily get hundreds, even thousands of individuals carrying the initial "D". I mean Ace also took the name of his mother just like that instead of that of his father. Law likewise only made part of his name known. So they all can very easily have been part of the same family 800 years ago and simply drifted apart during the course of the centuries. Considering different races like giants, humans and fishmen can provide offspring with each other, even that is not a reason to invalidate the possibility that all D's are related to each other.
So yeah it's very easily possible that all people who have the initial "D" originate from one and the same family.
That's I assume largely based on Enel's Space Voyage cover story where Enel discovered that there was once a race of people with wings on the moon who migrated to Earth because the moon was lacking severely in natural resources. The Skypieans and the people from the ancient civilization of Java are potentially their descendants considering they have wings and all and it might be a part of the story of the Void Century, however I doubt its at the center of it.
