I heard someone had done a 75 year projection for social security. Unfunded liabilities were in the tens of trillions, I dont recall the exact amounts. I think an unspoken additional assumption, is that government officials over the years, will make changes to address the issues before we get to the disasterous end point of such projections.
Actually, the opposite has been what has been done historically.
Government officials will spike the forecast to paint an unrealistic prediction of bright skies and wonderous financial growth that will fill the pension funds to overflowing.
George W. Bush tried to make changes to Social Security in his first year in office to avoid bankrupting the system. The Democrats stopped him at every turn.