You are wrong. Roughly 80% of all wages are covered, not 80% of all wage-earners....
well what's REALLY sad Archie, is the amount of time I spent trying to figure this out. What does it mean, actually, 80% of all wages?
anyhow, I did find some interesting links:
Contribution and Benefit base : https://www.ssa.gov/OACT/COLA/cbb.html
(from 1937-1950, it was $3,000; in 1971 it was $9,000; in 1986 it was $42,000 and since 2009 it's been $106,800)
Average & Median Amounts of Net compensation: https://www.ssa.gov/OACT/COLA/central.html
(average compensation has gone from approx. $20,000 to $39,000 from 1990 to present, and increase of 93.6% while median compensation has gone from $14,500 to $26,200 over the same period, an increase of 81%)
also: https://www.fairmark.com/retirement/socsec/social-security-tax.htm and https://www.calculatedriskblog.com/2010/08/social-security-benefits-and-maximum.html