If, in a retail installment transaction, a buyer makes any subsequent purchase of goods or services from a seller from whom he has previously purchased goods or services under one or more retail installment contracts, and the amounts under the previous contract or contracts have not been fully paid, the subsequent purchases may, at the seller’s option, be included in and consolidated with one or more of the previous contracts. Each subsequent purchase must be evidenced by a separate retail installment contract under this Act, notwithstanding that the purchase may be included in and consolidated with one or more of those in the previous contracts. All of the provisions of this Act with respect to retail installment contracts apply to these subsequent purchases except as otherwise provided in this Section. If installment purchases are consolidated, the seller may, instead of having the buyer execute a retail installment contract for each subsequent purchase as provided in this Act, prepare a written memorandum of each subsequent purchase, in which case Sections 3 and 14 and paragraph (a) of Section 5 do not apply. Unless previously furnished in writing to the buyer by the seller, by sales slip, memoranda or otherwise, the memorandum must set forth with respect to each subsequent purchase the following:
        (1) all items of disclosure required by Section 5 of