Home Slickdeals Costco Unadvertised Sales UPDATE for May 18th. While Supplies Last. Slickdeals Costco Unadvertised Sales UPDATE for May 18th. While Supplies Last. By ARCOM - 18 May 2022 42 0 SHARE Facebook Twitter Go to the deal page: Costco Unadvertised Sales UPDATE for May 18th. While Supplies Last.