For Billy's KoK tape, I'm going by the date Pigger has here
This is all performance dates, not verification dates.
The 1,047 tape was not seen or verified until Funspot in 2005, but it was recorded much earlier. Billy says in the movie that he'd been holding onto it for a long time. Also, the final score was engineered around beating Steve Wiebe's first submission (947K) by exactly 100,000 points. It seems like Billy wouldn't have made a big deal of targeting that score if Steve had already made his next few submissions by the time Billy played the game. 6/7/04 makes sense because Steve's 985, 995, and 1,006 all happened during summer '04 and would have been verified after 6/7/04.
I don't know where Pigger got his date, but I'll stick with it because we don't know how long that tape was lying around, but it was evidently months at least.
Thanks for the note about Tim Sczerby and the 1,024 being his first million, I didn't know Dwayne had that game archived too.