An appraiser prepared an appraisal report in April 2019. He testified in court regarding the value of the property in January 2020. The decision was rendered in February 2020 and was appealed in April 2020. The appellate court heard the case in January 2021 and remanded the case for reconsideration by the lower court. Final disposition of the case occurred in September 2021. At a minimum, how long must the appraiser retain his workfile?