The general bank will advise you to sign two copies, one for backup, but you can also sign only one copy, which is your freedom. However, if that is filled in incorrectly or the interest rate changes, you have to sign it again in person.
If it is normal, it is useless to back up the IOUs, and most banks will break them. Don't worry, the IOU is to match a series of materials and contracts, which contain your signature and fingerprints. In addition, a series of responsible persons will sign and confirm step by step, and have to pass the examination post. If it becomes an application file, it will be effective. It's no use just having an iou.