it's kind of a dilemma in that their games are usually based around your choices affecting the story, while at the same time not changing anything in the 'canon' story
with TWD they kinda did a side-story, and threw characters like Glen and Hershel in there. with The Wolf Among Us they went the prequel route. when this GOT game was first rumored, a lot of people were thinking prequel, and maybe something with Robert's Rebellion. but the little, and possibly inaccurate, info we got from the VGX interview was that it would be based on "the show". but other than that, it seems the Telltale guys weren't even really sure what it would be, or at least they didn't want to speak on it...