I did a quick review of past Mosconi Cup videos available on line.
It looks to me like the 9-ball has been racked on the spot at least since 2004.
For 1999-2003, the videos I could find make it look like the spot was under neither the 1-ball nor the 9-ball but in between them.
For 1998 and earlier, it looked like the 1-ball was on the spot.
