It is true that, in the run-up to monetary union (and bolstered by the Maastricht Treaty), there had already been a large measure of convergence in monetary policy thinking in Europe. That primarily affected the ultimate goal of monetary policy, and its institutional framework for achieving that objective.
But right up to the start of what was known as stage three of EMU, there remained national differences - some of them substantial - in the practical implementation of policies. To be sure, the now unified monetary policy of the Eurosystem has recourse in many areas to elements of the earlier national approaches.