Since section 13 is intended to protect funds or other property of all plans involved, bonds under this section shall allow for enforcement or recovery by those persons usually authorized to act for such plans in such matters. In most cases, the naming of the plan or plans as insured will provide for such recovery. Where it is not clear that such recovery will be provided, however, a rider shall be attached to the bond or separate agreement made among the parties concerned to make certain that any reimbursement collected under the bond will be for the benefit and use of the plan suffering a loss. Such rider or agreement shall always be required as respects any bond (a) where the employer or employee organization is first named joint insured with one or more plans, or (b) two or more plans are named joint insureds under a single bond with the first named acting for all insureds for the purpose of orderly servicing of the bond.