If a seller has not obtained an exemption certificate or all relevant data for exemption certificates for South Dakota sales and use tax, the seller may, within 120 days following a request for substantiation, either prove that the transaction was not subject to tax or attain a fully completed exemption certificate from the purchaser; effective July 1, 2007. The Department of Revenue need not consider any exemption certificate presented after the 120 days. (H.B. 1055, Laws 2007)