One of the worst things about the US social safety net, almost as bad as how weak it is even in total and in theory, is how piecemeal it is. Workers Compensation (and, for veterans, the VA) provide benefits that apply to partial and temporary disability, whereas Social Security provides benefits for only long-term total disability (that both prevents your past work and prevents transitioning to new work.) But evolution in jobs and working conditions, evolution in medical and assistive technology, and, frankly, refinement of knowledge about the initial injury can change what once seemed to be in one category to the other, and vice versa.