Social Security covers about 96 percent of all U.S. workers; the vast majority of the rest are state, local, and federal government employees. While these noncovered workers do not pay Social Security taxes on their government earnings, they may still be eligible for Social Security benefits.
I was a federal government employee, almost all before 2005 (date of your source), and paid social security taxes in
every pay period I worked. So this GAO report doesn't have its facts straight.
Some federal government employees
may have been grandfathered in to being exempt from social security taxes. Maybe that is who the GAO report is referring to. Just a guess on my part.
Also, if they're eligible for social security benefits (i.e.
While these noncovered workers do not pay Social Security taxes on their government earnings, they may still be eligible for Social Security benefits.), it would most likely be because they worked long enough in covered jobs where they paid social security taxes.