Was nominal GDP growth stable in the seventies?
The following chart shows nominal GDP and the trend.
It doesn't seem that much worse than the Great Moderation. The growth rates are substantially different. The trend growth rate of nominal GDP in the Great Moderation was 5.4 percent. In the seventies, it was 10 percent.
Using the CBO estimates of potential output, the GDP gaps were quite large during the period.
There is a pattern between the gaps between nominal GDP and the trend of nominal GDP and real output and potential output.
While the NGDP gap between nominal GDP and trend and the RGDP gap between Real GDP usually move together, it looks like treating the seventies as a period with a constant trend growth rate of nominal GDP is a mistake. Irresponsible out-of-control monetary policy is probably a better description.