(a) A retail installment contract may be contained in more than one document, if one is an original document signed by the retail buyer stated to be applicable to purchase of goods or services to be made by the retail buyer from time to time. In this case the document, together with the sales slip, account book, or other written statement relating to each purchase, must set out all of the information required by AS 45.10.030 and constitute the retail installment contract for each purchase.
(b) On each succeeding purchase under the original document, the sales slip, account book, or other written statement may at the option of the seller constitute the memorandum required by AS 45.10.100.