Mike mentions meeting Archie's parents during a recent visit. It would subsequently be established that Archie's parents had both been dead for at least 20-30 years.
In this episode Archie has no trouble saying "Reverend Felcher". Later in the series he can't help saying "Reverend Fletcher".
Revealing but not a mistake. The rug under the dining table is painted on the stage floor.
Archie says "I knew we had a couple of pinkos in the house, I didn't know we had atheists". On the two-part "Mike and Gloria's Wedding" (1972) Mike confessed that he was an atheist before they were even married.