The serial number would not have any thing to do with the sale of the bow! The serial numbers just tell the product line for PSE make ect. not when the bow was sold ! I work in automotive retail for Ford Motor Company! Some warranty`s starts at the date of puchase but the only way they would no that is if they ask you to send a copy of your reciept with yours mail in warranty. If they do ask for a copy of the reciept. I would call the PSE or there should be a number on your warranty form and tell them how you received the bow Im sure there will be no trouble! If they don`t ask for any thing else just post date it a few days before and mail it in.