I don't want to take away from Nick here, but I would like to clarify how the Rimington committee comes up with this "watch list".
Unfortunately, they don't watch game film on every single center and critique each one on footwork, technique, line calls, etc. While this would be the method that would yield a list that truly represent the best centers in the college game, it is just much too time consuming and requires people with a specific knowledge set.
Instead, the Rimington committee looks at one thing above all others...number of games started. They figure that those players who have seen the field the most (ie. started early in their college careers) are the most likely group to contain the single best center in the nation. This explains why the vast majority of centers on the Rimington Watch List are upperclassmen every single year.
In other words, this "watch list" isn't about identifying the best 42 centers in the college game. Rather, the committee's goal is to identify a quick, inexpensive method that will yield a group of players who will likely contain the true best center. In the end, all that really matters is that the Rimington award winner at years end was actually on the "watch list" before the season began. This method yields that result on a consistent basis.