Here is the answer I received regarding these questions.
There is a slight difference between each overall point a player goes up by. We usually interpolate when running any logic in Franchise. So an 82 would have a slightly less chance of doing something than a 83.
Player types dictate overall for players so a Defensive Defenseman is going to have different overall formula than a sniper. For example, a defensive D takes into account more Defensive stats vs Sniper which takes into account more shooting/offense. Additionally if the player is playing out of position they get penalized unless it's considered a secondary position.
Additionally a Players development is determined by their Potential.
I hope this helps.