This indicates to me that there can be significant and persistent deviations in the equilibrium real rate from the observed long-run average measured over decades. The average interest rate that seems to have brought aggregate demand and aggregate supply into rough balance in the past may not be the same rate required in every conjunctural setting.
Our inability to equate the long-run average interest rate to the equilibrium real interest rate that is relevant for setting policy is not surprising given the manner in which economic behavior, technology, and government policy can change over time. Put another way, an estimate derived from long-run observations may not be relevant for policy for two reasons.