def sv_validate_priority
    unless self.type_class.nomenclatural_priority.nil?
      date1 = self.subject_taxon_name.cached_nomenclature_date
      date2 = self.object_taxon_name.cached_nomenclature_date
      if !!date1 && !!date2 && date1 > date2 && subject_invalid_statuses.empty?