If it says Active in the Addon Manager, it's normal that it won't ask any keys because...it's Active! The activation stays forever, even if you uninstall GSX, uninstall the sim, etc.
The only way to lose an activation is reinstalling Windows from scratch, or change major hardware component, like the CPU or the mainboard. Not even changing the video card will result in losing activation so, apparently, you activated previously, so it's still there.