That is a tricky one, but of course, datum is hardly ever seen or heard, and data is generally considered either plural or singular. :') Commander Data had at least two twin brothers (Lore, and I forget the other one, which was introduced in Star Trek X; XI is in the works I just heard) but they didn't have his name. Data built his own child, Lal (I think the name was), but that was a daughter. And there was another Soong android, but of course, this is a pretty geeky thing to discuss in a topic about a 9,000 year old dead guy. ;')
And, a discussion of 9,000 yo dead guys isn't geeky?