A couple of times I forgot to check-in at the precise 24 hour mark and checked-in maybe 2 or 3 hours into the 24 hour window and maybe got B-27 or B-41, but I've never gotten a letter C. I guess I've been lucky. I make it a point to sit at the front of the plane but avoid the middle seat. If only middle seats are available in the front I try to find a window or aisle towards the back. It's always amusing to watch newbies coming on the plane and claiming a front seat but not having any overhead bins to store their bags so they store their bags further back in the plane and sitting in the front. When arriving at McCarren though I always want to get off as fast as I can (lol).