Genealogists routinely make the mistake of assuming that the father-of-record is necessarily the biological father.  However, this is not always the case in polygamous Mormon culture, as wives are officially and unofficially shifted from man to man.  Even sisters have been traded.  We will never really know the full extent of what went on in the Mexican Mormon colony the Romneys sprang fromof course, that was precisely why the left the United States to begin with.  It makes sense, of course, that Romney and his political operatives would want to keep these issues from the American people.