When Archie mentions his cousin Oscar, Mike behaves as though he didn't know anything about Oscar's visit to the Bunker house. In The Saga of Cousin Oscar (1971), Mike was living with the Bunkers at that time, and in fact was the one who discovered Oscar had died in the attic. The older episodes of this series had been shown on weekdays in syndication for over a year when this episode was taped; the writers should've realized this conversation would contradict "The Saga of Cousin Oscar" (1971).
At around 21 minutes when Archie knocks on the bedroom wall to speak to Edith, he is clearly knocking on an exterior wall. This based on the layout of the home and the fact that their bed sits between two windows.
Based on the layout of the doors in the hallway (three doors at 90-degree angles at the top of the stairs) it becomes clear that the layout of the bedrooms is physically impossible. The size and shape and orientation of the rooms could not exist in the house as shown.
Per the Merriam-Webster dictionary loan is a verb as well as a noun so Archie was correct. Mike should have known this with his college degree.