The service charge allowed in section 51-14-03 shall be allowed to a seller or holder only:

1.    If the seller enters into an agreement subject to the provisions of this chapter with any buyer on or after July 1, 1959; or

2.    In the case of any buyer who had entered into an agreement with a seller prior to July 1, 1959, if the seller or holder delivers or mails to the buyer a copy of a retail installment credit agreement in conformity with this chapter duly executed on behalf of the seller and the seller or holder thereafter complies with all the other provisions of this chapter.

Nothing in this section contained may be construed to affect the validity or invalidity of any agreement or alleged agreement made prior to July 1, 1959.