I understand that but DMR members are allowed to redeem one code per title, per format. Therefore, potential bidders need to have both pieces of information in order to know whether or not they can use the code. If you don't know then I would recommend that you list as a random or mystery code but they normally don't do as well since the bidder is taking a risk.
Without both pieces of information your listings will also be repeatedly flagged for review by the moderators for "Not Enough Information" which could lead to disciplinary action. Good Luck.