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. Global trade flows collapsed in the spring, marking the largest fall in two decades, as coronavirus lockdowns disrupted air and sea transport and dealt a blow to the demand for many consumer and investment goods. In more recent weeks, signs have emerged of a rebound in the movement of goods across national borders. But the enormous economic and social disruptions caused by the pandemic are expected to reshape global trade in the longer term. …