To the extent permitted by federal law, no contributions shall be due from any nonprofit organization which first became compulsorily subject to this part on January 1, 1978, by reason of the enactment of the federal “Unemployment Compensation Amendments of 1976” (Public Law 94-566) and the amendment to Section 634.5 by the 1978 portion of the 1977–78 Regular Session, which elects a method of financing under Section 803 when such election first becomes available, but not later than April 1, 1978, and which also elects to use contributions paid pursuant to an elective coverage agreement of such nonprofit organization in effect prior to January 1, 1978, until the cost of benefits paid and reimbursable by the nonprofit organization together with the benefits charged and chargeable to the reserve account of the nonprofit organization as the result of its prior elective coverage agreement exceed the contributions made by the nonprofit organization and credited to its reserve account pursuant to its prior elective coverage agreement.