27 CFR §40.435

All records and reports required to be kept or maintained under this subpart, including copies of authorizations, inventories, reports, returns, and claims filed with verified supporting schedules, shall be retained by the manufacturer for three years following the close of the calendar year in which filed or made, or in the case of an authorization, for three years following the close of the calendar year in which the operation under such authorization is concluded. Such records shall be made available for inspection by the appropriate TTB officer upon request.