The ledge outside the windows wraps around from one apartment to the next. However, in episode 4x03 Lucy climbs out of the window from her apartment and the ledge only appears on that side of the building and doesn't wrap around the adjacent side.
When Carolyn and Lucy are arguing over which son was born closer to Saturday, Lucy says that Little Ricky was born at 11 AM. But we all remember that Little Ricky was born at night while Ricky was performing at the Tropicana.