We don't recommend doing any correction on the pink slip unless the seller can autograph it. The DMV should process this Honda Civic's title transfer based on the date on the Bill-of-Sale. The official purchase date should be the one indicated on the Bill of Sale. Often sellers are convinced of a purchase, prepare the vehicle's title for purchase, only for the deal not to go through. The seller should make the correction on the title and indicate the correction with their initials or signature.
If it's too late to contact the seller, don't worry about correcting the title. Simply explain the situation to the DMV clerk and make sure your have a bill-of-sale with the CORRECT purchase date.