Currently, you'll know after the first TC if a player will trend up or down. It sounds as if down the road a downward trending (and vice versa) player by retrending upward if they move on from team to team.
Is the chance of booming or busting equal, or is there a tendency to either side?
It's supposed to be about 50/50 but keep in mind players that start out as a 100 in everything can't improve if they boon, so the best you can hope for there is that they stay the same.