Yup and that is why they pay the scouts the big money. The player that most recently sticks out for me was Josh Jackson at Iowa. So many were enamored by his 8 interceptions, 2 of them returned for TD's. Many thought he had earned himself a potential first round grade. A few scouts noticed that he really wasn't very good man to man. I will admit that I thought he was a steal for the Packers in the second round at #45. Turns out, the guy was completely overrated and appears to already be out of the league. Then there are the guys who have a huge sack total in their contract year and someone pays them big bucks as a result. Usually, to find out that all those sacks really didn't define the player very well.
Obviously, there are other factors, such as injuries, coaching and the dreaded "I got paid big, I'm set, I can coast now". I think that was one of the reasons TT stayed away from big Free agent signings as much as he did. He didn't want to over invest in a player that other teams were offering way too much money to.