{Putting on pedantic hat] Let's see...data is the plural form of datum, so how many Data were there on that series?
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 of course, as Data said, "one is my name. The other is not." :'D