We have paid non-resident fees which get used for unique patron codes which last 1 year. If a customer is renewing their registration early, we give them a year from their expiration date so that they are not losing any of the time that they previously paid for. Perhaps a checkbox in the renewal dialog box to indicate that this is what we want to do, but also an option to have this automatically toggled for certain patron codes and an option to suppress its use when an account is fully expired.