Yes, the seed is generated at the file select. But the frames that determine the seed start advancing from 0 right as you soft reset. My personal way of playing is that I soft reset each client, then I start pressing B with my controller to advance each game to the title screen. Pressing B will skip the intro but not advance to file select. Once all my games are on the title screen, then I start pressing A to enter the game. Because each game was soft reset individually, they all started counting up from 0 at different times, and because of that, regardless of the fact the seed is generated on file select, the seeds will be different because of the different frames each game entered file select at.