Scouted once: Your scouts have seen this player play one game, and have provided the player's boxscore for that game, as well as an initial assessment of his current skills.
Scouted twice: Your scouts have invited this player to a workout at your team's facilities. Along with all of the information you have learned from the initial scouting, you now have a better understanding of this player's current skills (grade rating), as well as insight into his potential abilities. You also discover whether the player is 18 or 19 years old.
Star power=initial assesment, overall initial grade
Grade Rating=Current skills
Potential=How much potential he has for improvement (abstract answer, see training)