apologies if my understanding is too simplistic, but is this correct?
1941-1951 JSA was main earth's team of superheroes
1951-1961 No JSA around
1961-1985 JSA was Earth-2's version of the Justice League, with regular team ups between the JSA and JLA when the multiverse was threatened.
1985-1991 JSA didn't exist?
1991-1999 JSA was the main Earth's first superhero team, years before the JLA was formed
1999-?????