Mich. Comp. Laws § 445.856
A retail installment contract shall not be signed by any party thereto when it contains blank spaces of items which are essential provisions of the transaction, but if delivery of the goods is not made at the time of the execution of the contract, the identifying numbers 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. The buyer's acknowledgment, conforming to the requirement of subsection (b) of section 3, of delivery of a copy of the contract shall be presumptive proof, or, in the case of a holder of the contract without knowledge to the contrary when he purchases it, conclusive proof of such delivery and of compliance with this subsection and any other requirement relating to completion of the contract prior to execution thereof by the buyer, in any action or proceeding.
MCL 445.856