(a) Entire agreement.--Except as provided in section 6329(c) (relating to add-on sales), a closed-end credit agreement shall contain the entire agreement of the parties regarding the costs and terms of payment for the goods and services, including a promissory note or other evidence of indebtedness between the parties relating to the transaction.
(b) Signature.--A seller may not obtain the signature of the buyer on the agreement if the agreement contains blank spaces to be filled in after it has been signed.
(c) Installments.--A closed-end credit agreement may provide for unequal or irregular installments.
(d) Incorporation by reference.--A holder may, in a buyer's subsequent closed-end credit agreement, incorporate by reference the buyer's previous closed-end credit agreement and a description of the collateral for the items purchased under the previous agreement.