At one point when Lucy is standing at her front door, Ethel comes walking by. However, Ethel comes from a point that would be outside the Ricardos' window. (And the hallway could not bend right next to the window, as we have seen at other times an outside ledge running for quite a ways parallel to the window, as in "Lucy Cries Wolf" and "Lucy Meets Superman".)
Since the apartment building belongs to Fred and Ethel and in other episodes they seem involved in the rental process (even if they use an agent) shouldn't they know far more about The Johnsons than they do? For example Ethel only knows their last name at the beginning of the episode. Even in the 1950s apartment owners had to look into the background of their potential renters but Fred and Ethel appear completely unaware who is moving into their building.