Where a buyer makes any subsequent purchases of consumer goods from a seller from whom he has previously purchased goods or services under one or more conditional sales contracts, and the amounts under the contract or contracts have not been fully paid, the subsequent purchases may be included in and consolidated with one or more of the prior contract or contracts. A memorandum of the additional purchases shall be prepared by the seller, inserted in or attached to the seller's counterpart of the contract and shall set forth:
(a) A description of the additional goods or services so purchased;
(b) The consolidated total indebtedness of the buyer;
(c) The finance charge stating either as the additional amount on the subsequent purchase or as the total amount on the consolidated contract;
(d) The revised installment payments. A copy of the memorandum shall be furnished to the buyer.