In the event that the decision has not been communicated to the competent authorities within the period provided for in paragraphs 6c or 16, the competent authorities may agree to extend that period for a period not exceeding six months or, if they fail to do so within one month from the end of the period provided for in paragraphs 6c or 16, they shall appoint a new arbitrator or arbitrators in accordance with paragraph 5 or 6a, as the case may be.
