(e)     that are not used by a distribution cooperative to satisfy the renewable portfolio standard or that are not traded, sold or otherwise transferred by the distribution cooperative may be carried forward for up to four years from the date of issuance and, if not used by that time, shall be retired by the distribution cooperative; and  

(2)     a distribution cooperative shall be responsible for demonstrating that a renewable energy certificate used for compliance with the renewable portfolio standard is derived from eligible renewable energy resources and has not been retired, traded, sold or otherwise transferred to another party.