Kat, thanks for becoming a fan! As to a response to your piece, when grading cornerbacks (or any position), I only grade them when they play THAT position (unless you have say a RB playing WR or a DE playing OLB). I don't take into account their ST work because that's covered in Special Teams (where I don't grade players individually unless they have an exceptional day).
Secondly, I don't grade based off of the whole season, I go from game to game. There have been days when Nolan Carroll has done well, and he's gotten the proper grade for THAT DAY. From one game to the next, the slate is wiped clean, with no season-encompassing grades until I do the End of Season report card (which will come the Monday morning following the final game of the season). Look in the archives and you will see this.
So to say that Carroll deserved higher than a C for Sunday's game based off of what has happened the whole season doesn't fit with the report card itself. Playing time doesn't matter either, it's what he does when he's on the field. From what I saw in that game, Staford had the better performance. Once the NFL's All-22 cam version of the game comes out later on, then I review it (as I do for all games) to see how spot-on my grading was since you don't always see every player on every play (and this is more true on defense since the cameras follow the ball).
You're entitled to your opinion on CB's, as am I. From what I saw Stanford did B work when he was at corner, while Carroll did C work. Either way I'm sure we can all agree that cornerback is a position of need for the Dolphins this offseason.