The overall quality which is what determines the star rating of a player, is an average of Attack, Defence, and Physical attributes.

Ie, a player will be 70 rating if he has 70 Att/Def/Phys, or 75 Att, 60 Def, 75 Physical. Basically add all three together and divide by 3.

It takes 5 Skill points to raise each Atrribute (Att/Def/Phys) by one, therefore it takes 15 skill points to add 1 overall quality to your player.

Players will gain a star rating when their quality ends in 0 or 5.

I think you have been confusing overall quality with each attribute.

Ie. just because a player has gone from 63 to 65 defence doesn't mean he will gain 2 overall quality.