code: def update_date_year(self):
          
          dates = record_get_field_instances(self.record, '260')
          for field in dates:
              for idx, (key, value) in enumerate(field[0]):
                  if key == 'c':
                      field[0][idx] = ('c', value[:4])
                  elif key == 't':
                      del field[0][idx]
          if not dates:
              published_years = record_get_field_values(self.record, "773", code="y")
              if published_years:
                  record_add_field(
                      self.record, "260", subfields=[("c", published_years[0][:4])])
              else:
                  other_years = record_get_field_values(self.record, "269", code="c")
                  if other_years:
                      record_add_field(
                          self.record, "260", subfields=[("c", other_years[0][:4])])
docs: 260 Date normalization.