Notice in the flashback scene how the front walls of the Bunker house still have the new wallpaper that Edith had put up after the house had caught fire near the end of the previous season.
The two Klan leaders' names, "Gordy Lloyd" and "Mitch Turner", are obviously based on Lloyd Turner and Gordon Mitchell, two writers who had worked on previous AitF episodes.
If you look carefully at the scene where the customers come into the bar for the opening, a couple comes in at the beginning of the show, they are celebrating their anniversary. The wife has NO speaking role, and therefore she is not mentioned in the credits. However, she is none other than Doris Roberts (who many years later starred on Everybody Loves Raymond.) Ironically, Doris Roberts HAD been on an earlier episode of All in the Family, with a short, credited speaking role, two years earlier, Season 6, Episode 24 "Edith's Night Out", as a bar patron in the same bar before it was owned by Archie.
Nitpick – Archie says that Gloria was nearly attacked by the construction workers three years ago. While certainly it's normal to fudge on the number of years that something like that happened, that incident actually happened four years earlier (in the 1973 episode, "Gloria the Victim").
Who are the "guests"? The only one we recognize is Sybil Gooley. Where are the Jeffersons or Lorenzos or Cousin Maude or Cousin Amelia or any of Edith's other friends or relatives who surely would have attended her 50th birthday party. (Of course it would have been too expensive to get everyone, but a few more familiar faces would have been appreciated).
Shortly after Veronica reveals the true nature of her relationship with Liz, Edith says "That don't affect the brain, does it?" The camera angle then changes, and the shadow of the boom mic is visible to the left of Liz's head, then it moves upward and out of the screenshot.
Cousin Liz and Veronica's apartment appears suspiciously similar to the Jeffersons' East Side Condo!
The shade on the living room window by the staircase is completely down during the breakfast scene when Archie comes into the room. Moments later, when Edith is arguing with Archie, it is raised all the way and the sunlight is visible, even though no one has gone by the window.
This two part episode was the final appearance of the recurring character Tommy Kelsey. However, Bob Hastings, who had played the role for the entire series, apparently wasn't available for this episode and the role was recast.
Since Mike barely knew Oscar it would indeed be possible to forget the guy. Archie himself didn't know much about Oscar and he was his cousin. I have plenty of cousins that I've met but wouldn't know them if I tripped over them.
Mike asks Archie who's Cousin Oscar, who is the cousin that died under the 704 roof back in Season 2. The goof is, Mike and Gloria were under the roof back then and they even attended the funeral which Archie hosted--how can Mike not remember?
When Edith looks in the bathroom the bathroom layout and fixtures are different. In the episode Birth Of The Baby part 1 the toilet is beside the bathtub, and the fixtures were different but in this episode the toilet is beside the door on the left and the sink is on the right of the door.
In this episode only, the bathroom is set where Gloria and Mike's (and Stephanie's future) bedroom is in every other episodes, instead of being in the far back of the hallway.
This episode consists of one continuous scene aboard the subway.
William Pierson, who plays the wino in the subway car, was best known for his recurring role as Dean Travers on Three's Company
Archie learns from Stretch Cunningham's obituary that his first name was Jerome.
Archie reveals that his favorite brand of beer is Schlitz when the art critic asks how he antiqued the fabric of his chair.
During Archie's toast, he makes a toast to Joey "who's upstairs taking a nap.." and he goes on to say that that's why they are able to enjoy their Christmas in peace...
This episode was among Norman Lear's favorites of the series.
Mike's moustache looks strange in this episode. It looks like he had shaved and they had him wear a fake one.