Stock and Watson (2010) say that “there are some hints that the slope parameter might be smaller at low levels of inflation but these hints are not robustly confirmed by statistical tests”. Stella and Stock (2012) even find signs of a steepening of the Phillips curve for the United States.
However, the main point here is not that these decisions were validated in hindsight, but that, 3/7  BIS central bankers' speeches  once the need to take action had been substantiated and justified, the courage was found to take decisions, without hesitation, for the benefit of Economic and Monetary Union.