private void ClearPreviousMatches(string MatchType)
    {
      if (PotentialMatches.Rows.Count == 0) return;

      //wipe out existing matches in a group, because each batch should be considered an entirely new list of hits
      using (DataView v = new DataView(PotentialMatches))
      {
        v.RowFilter = "MatchType = '" + MatchType + "'";
        v.ClearRows();
      }
    }