N.C. Gen. Stat. § 106-9.5

If the Commissioner of Agriculture discovers from the examination of any report, or otherwise, that any taxpayer has overpaid the correct amount of any fee or tax (including penalties, interest and costs, if any), such overpayment shall be refunded to the taxpayer within 60 days after it is ascertained together with interest thereon at the rate of six percent (6%) per annum: Provided, that interest on any such refund shall be computed from a date 90 days after date tax was originally paid by the taxpayer. Provided, further, that demand for such refund is made by the taxpayer within three years from the date of such overpayment or the due date of the report, whichever is later.