It excludes corporate defined benefits pensions. I suspect the people on corporate defined benefits is fairly low at this point.
Source of the social security number? I have a salary above average, and the SS web site estimates a $24K/year for me (today's dollars). Lower income folks should get less.
The minimum benefit for someone who worked 30 years making minimum wage is $872.50 per month, 10.5k/year The maximum benefit is $2,861 per month or 35k/year, for someone who made 140+k for 35 years.
PIA formula For an individual who first becomes eligible for old-age insurance benefits or disability insurance benefits in 2019, or who dies in 2019 before becoming eligible for benefits, his/her PIA will be the sum of: (a) 90 percent of the first $926 of his/her average indexed monthly earnings, plus (b) 32 percent of his/her average indexed monthly earnings over $926 and through $5,583, plus (c) 15 percent of his/her average indexed monthly earnings over $5,583.
Note the c is capped 11,075 US$ per month as income above that is not taxed.