In recent years, purchasing managers indexes have become important indicators of where the global economy might be heading. But in the current slowdown, where small businesses were some of the hardest hit, PMI numbers may not be telling the full story. WSJ explains. Photo: Getty Images Factories had a big rebound last month, but Covid-19’s resurgence is threatening to cut the manufacturing recovery short. The Federal Reserve on Wednesday reported that industrial production—the combined output of U.S. factories, utilities and mines—rose 5.4% in June from a month earlier after a 1.4% increase in May. The gain was driven by a 7.2% increase in manufacturing production, with a 120% jump in motor vehicle output counting as the standout. …