To be clear, I'm pretty sure no one here will answer correctly with that much specificity. The people who know the answer are under NDA and will not talk here.
Well, there are only so many places you can get that kind of data, and none of them are secrets. SABRE is by far the most comprehensive for flights originating in the US.
Right, so you don't have actual knowledge, you're just speculating.
As someone who worked in the industry, I would seriously question your claim about Sabre. In any event, note that ITA deals with global flights, so flights originating in the US are only a portion of what they need.