§ 12. Nonschedule adjustments. Notwithstanding any other provision of this chapter, in any case coming within the provisions of sections ten and eleven of this article, in which the right to benefits has been established and benefits have been paid for not less than three months, in which the continuance of disability cannot be ascertained with reasonable certainty, the workers' compensation board may, in the interest of justice, approve a nonschedule adjustment agreed to between the claimant and the political subdivision liable for the payment of benefits or its insurance carrier. The provisions of subdivision five-b of section fifteen of the workers' compensation law shall apply in any such case.