User blog comment:Тостер/Scraping the Bottom of the Rogues Gallery, Part 2: Green Arrow's Rouges Gallery/@comment-27700324-20161029020913/@comment-1854917-20161029044109

It is true, but they still appeared on Arrow first. Boomerang was not even appearing on The Flash, only being mentioned here, which, I think, is a part of a tendency considering how Murmur and Double Down were only seen on Arrow as well - it's just that seeing some of the Flash villains many people don't know why the belong here - his/their Rouges Gallery is quite a surreal one.