815 ILCS 405/15

Notwithstanding Sections 4 and 5 and paragraph (a) of Section 3 of this Act, if delivery of the goods is not made at the time of the execution of the retail installment contract, and the contract so provides, the identifying number or marks of the goods or similar information and the due date of the first installment may be inserted by the seller in the seller's counterpart of the contract after it has been signed by the buyer.