CVG just came out with this story: CVG: GTA 5 will not be shown at Gamescom
I'm still a firm believer Rockstar will use the event as a stage to show their game to retailers and publications. All this means is they'll have no public presence such as the rumoured second trailer, which is really no surprise.
The fact that it took them a month to correct the "error" in their trailer is suspicious enough. I've put together media packages before and I know that when making a trailer every piece of footage is chosen carefully. The fact that the GTA V footage was on the trailer in the first place suggests some kind of presence, official or otherwise. Big things like this do not just slip through the cracks.