because the whole crew is there as witnesses and the lottery officials immediately telephone the print and radio media outlets to tell them the numbers which were just broadcast. There's at least two lottery officials who do everything together at all times. So, no one can rig it.
Also, some stations carry it live. On the satellite feed, all the affiliate stations don't even see the practice draws so there won't be any confusion. The control room at the studio station doesn't hit the video switch for the "bird" until they are in the countdown for the real thing. The practice draws and the videotaping of the practice draws are for the lottery officials only. But, the point is there's really several drawings -- but the one that hits at 10:58:00 EST is the official one. So, if you have some sort of mathematical formula going, maybe you won a practice draw. :)
Also, if you are trying to have a mathematical scheme going -- your database has incomplete entries. Only the lottery officials know ALL the numbers that have come up. The public is only seeing one drawing. If you had ALL the numbers, and if you knew which set of balls were being used and what their past history was, and which tumbling machine, then you might have a chance. Until they discarded that set of balls and replaced it with a fresh set -- the way a baseball umpire thows in a fresh baseball. In fact, all these practice draws are like innings, in a way. And everyone's mathematical scheme is based upon the ONE inning the public gets to see -- whereas you need to know ALL the pitches thrown against left- and right-handed batters for the whole game.