In "The Chicken Roasters" episode both Jerry and Kramer have windows overlooking a street. Could not happen. One of them (probably Kramer's) would be overlooking a courtyard.
Saw an episode last night that showed a distance shot of the hallway, facing towards Seinfeld's and Kramer's end of the hall. It looked like a fairly typical square, dead end hallway to me, completely unlike the floorplan above.
Further, it was completely incompatible with the layout of the Seinfeld apartment's kitchen/front door arrangement.