I'm not sure that potential labour force growth is today similar to the 70s, U.S. median age 28, 80s U.S median age 30, and 90s U.S. median age 33. The median age is now 38.2 in the U.S. and the rate of labour force growth has fallen as a result. In the context of the G7 the U.S. is in good shape. Germany & Japan's median age is well over 48 and their labour forces are shrinking. If potential nominal GDP is truly labour force growth + productivity growth + inflation a smoothed series points to potential NGDP of around 3.2% for the U.S. and much lower for Germany and Japan. For some reason countries with aging populations seem to have low inflation/deflation.