I think that perhaps if you train on a long run the same players, you will have initially a normal distribution of the extra pops, due to all the skills that are near to the pop (x.9 decimals) and then you will see a decrease because the other skills are far from the pop and you will need lot of luck to have the same skill and the same player choosen several times to have the pop.
For example, if a player is x.6 he needs to be choosen 4 times which is a very lucky case.
I have seen few players having two extra in different skills, but never two extra in the same skill for the same player