Rabiator here (same forum name as in Firefall). Can't remember the exact date I joined Firefall, but I remember I snatched a closed beta key. My oldest post on the FF forums where I talked about my observations in-game was
this. So I certainly was already a Firefall player on Aug 15, 2012.
BTW, I just visited Firefall again, starting after login at Shantytown, where I was last leveling my char. It was pretty deserted. I flew around for a bit and tried to defend Skydock when the usual call for help came in.
But there was nothing to fight. Skydock was just bugged again, and pretty deserted too. I met one other player who was also responding to the Skydock alert, and we ran around the otherwise deserted Skydock for a bit. Somewhat sad, I logged out again...