Going back through the Shot Show videos of the Kel-Tec booth on YouTube - there were only a couple of comments on the release date:
"Later this year"
"Toward the end of the year"
"At the end of the year"
I didn't even hear them qualify the time frame as 4th quarter.
Kel-Tec posted a video on YouTube to follow up on the Shot Show, which was posted on February 28th. In that video Chad says "[Kel-Tec] will be shipping [the KSG] at the end of the year." So my guess is that the very earliest would be October, but it could be December.
Here is the link to the Kel-Tec YouTube video: