From the IMF´s Making Monetary Policy Decisions in the Dark:
In the wake of the global financial crisis, monetary and fiscal policies were used aggressively to counteract the effects of the crisis on economic activity. Policymakers look at a number of indicators to guide them in assessing an economy’s level of activity relative to its productive capacity. But trying to figure out the position of the economy in real time is often quite challenging, with consequences for setting policy.
Obviously, they didn´t look at the one that “tells it all”! That´s NGDP growth falling way below trend!