Most of the "leaks" are just documents that had been leaked elsewhere and circulated around the internet for years previously, that got reposted and reported without context.

Pretty much. The reason why these "leaks" get mentioned so much is because the idea of leaking classified documents on a video game forum is mildly amusing. The game is popular among people enrolled in the military, so it's not implausible that someone would leak documents for laughs and clout.