In fact, as Richard Koo demonstrated WRT Japan since 1990, the slope of the line can drastically change and the starting point of any new growth can be at or below the maximum level reached before the contraction began. That is how you get "lost decades". The foregone production, if considered as the integral of the volume between a projection of the original growth line and the actual rate experienced, may never even close and may expand indefinitely.

I think that is almost certain to be the case for decades in the USA, whether the slope is taken from the growth rate prior to 1970, 1990, 2000 or 2007. I guess the "mainstream" can just keep redefining the slope forever in preference to admitting their assumptions are fallacious.

"It is not necessary to have hope in order to persevere."