zanzibar: It's likely that the games of the two have been combined.
The Argentinian is currently inactive, with the higher rating of 2000 (despite being younger - dob 1958 vs. dob 1949).
That would make the 2013 player the American (rating 1981).
Most likely the US and Canadian events are the American, and the Argentinian events (32nd Open and Mar del Plata) are the Argentinian.
The American seems to travel to the senior tournaments, as said, the 2013 tournament due to active status, and the 2011 tournament as shown here:
The Argentinian has been inactive since 2010-May according to here:
Gheesh, I hope there aren't too many more of these cases around!