Even if some Japanese refiners resume Iranian oil purchases thanks to the U.S. waiver, refiners have just a small window to clear all related transactions, so they are likely to finish loading potential cargoes from Iran by the end of March 2019, uncertain that their waiver will be extended beyond May, industry and trade sources tell S&P Global Platts. Japan was one of eight Iranian oil customers who received a U.S. waiver to continue importing Iranian oil at reduced volumes for 180 days after November 5, the day on which the United States…