20 C.F.R. § 726.5
Pursuant to section 422(c) of part C of title IV of the Act, no coal mine operator shall be responsible for the payment of any benefits whatsoever for any period prior to January 1, 1974. However, coal mine operators shall be liable as of January 1, 1974, for the payment of benefits in respect of claims which were filed under section 415 of part B of title IV of the Act after July 1, 1973. Section 415(a)(3) requires the Secretary to notify any operator who may be liable for the payment of benefits under part C of title IV beginning on January 1, 1974, of the pendency of a section 415 claim. Section 415(a)(5) declares that any operator who has been notified of the pendency of a section 415 claim shall be bound by the determination of the Secretary as to such operator's liability and as to the claimant's entitlement to benefits as if the claim were filed under part C of title IV of the Act and section 422 thereof had been applicable to such operator. Therefore, even though no benefit payments shall be required of an operator prior to January 1, 1974, the liability for these payments may be finally adjudicated at any time after July 1, 1973. Neither the failure of an operator to exercise his right to participate in the adjudication of such a claim nor the failure of an operator to obtain insurance coverage in respect of claims filed after June 30, 1973, but before January 1, 1974, shall excuse such operator from his liability for the payment of benefits to such claimants under part C of title IV of the Act.
20 C.F.R. §726.5