Green Arrow began publication in 1941.
I first read about GA in 1956-1960.
The Dark Knight Returns was published in 1986; The Longbow Hunters in 1987.
GA first appeared in Smallville in 2006.
GAY1 was published in 2007.
Arrow began in 2012 and is on-going.
The Wiki article reveals an incredible history of changed continuities.
I am watching Smallville and Arrow dvds and have started to reread The Longbow Hunters and GAY1. IMO, these and DKR are the most significant GA continuities.