DL does seem to be blocking 2 or 3 seats at the front of the Y "cabin" on some aircraft before check-in opens. I'm not sure it is the case on all aircraft, but if you do a dummy booking out lets say 270 days, you'll probably see two seats unavailable at the front of C+ and two at the front of Y. Like this photo. IMO 14 DE are at slightly higher risk of you being moved than other seats if you've managed to be placed in them ahead of time.