I don't believe players are deliberately overscored, but I think it's possible certain players might be more prone to getting the "good" stats more than others.
Like Nank, I reckon a few of his HTAs registered might be a bit questionable, but as he has a good reputation for getting them at CD, he probably gets the benefit of the doubt most times.
Similarly, guys like Pendles or Bont who kick to a contest and the opposition takes a mark, if the CD scorers record the opposition as taking a contested mark, no clanger, but if it's an uncontested mark, it's a clanger. So with their reputation for good ball use, perhaps the scorers might be inclined to think that they kicked it to a contest and thus they avoid the negative points. Small things like that can add up due to the inevitable subjectivity in decisions. It's all part of the game.