This is MY theory, and I don't know if it's true, but it seems logical to me:
I think every position has a formula whichj uses a factor for each skill. Depending on the position some skills tend to get more important, and get bigger factors.
If you calculate the player for every position, you can see which is the highest result, and according to that, he is given his best position by BB.
Therefor, after training a specific skill, a player might get an other best position...
example:
Let's assume for this example that the PG's most important skills are passing, handling, outside defense and driving.
And a SF's most important are jump shot, passing, handling and driving.
3 of the skills are the same, and the player is good in all tree, and he's also prety good in handling, so the result of the calculations of the 5 positions is in favor of the point guard, but the result for SF is only a little lower.
After training jump shot ( the factor for the SF for his jumpshot weighing more heavely than for the point guard) the result of the calculation for the SF might become slightly higher than for the PG, making him a SF all of a sudden....
They are not your friends; they dispise you. I am the only one you can count on. Trust me.