The background in the Kramden's window changes. Sometimes there are windows and fire escapes. Other times the fire escapes aren't there. This happens within episodes, not just from one episode to another.
The door knob on the door to the Kramden's apartment is usually seen on the right side of the door. However, in certain episodes, the doorknob is shown on the left side of the door.
The Kramden's are said to live in the Bensonhurst section of Brooklyn. Their address is referred to , in several episodes, as 328 Chauncey Street. That address, however, is actually in the Bushwick section of Brooklyn.
The Kramden's apartment door opens out into the hallway. A door that enters a dwelling always opens into the building...such as apartments, hotels/motels, and houses.
The background behind the stove and the window were actually curtains. There are a few episodes in which the corner (where the two meet) would separate and you could see a little of what was behind it.