When you take a look to the skills of your players, you can see a number, for example:
Inside defense= 7
But this number can be 7.1 or 7.5 even 7.9, and you don´t know which sublevel of each skill has your player. When you train him this skill, he may improve to the next level(8) if he had 7.8, or maybe 7.5 from 7.3 and you´re only going to see 7 again.
The numbers that i put were not real, it was an eample.
Best regards