A base listing document shall be valid for a period of 12 months from the date on which it is published or (if earlier) until such date as the issuer submits its annual accounts to the Exchange in accordance with rule 15A.21 whereupon an issuer must file a further base listing document. A base listing document may not be amended without the prior approval of the Exchange. A base listing document may be amended to allow the inclusion of Interim Reports or quarterly reports.