Defictionalization: Several things, but perhaps most prominently the "Silly Party" of the Election Night Sketch inspired the Real Life Monster Raving Loony Party. The Overly Long Name of a candidate was also borrowed by a real British election candidate.
In the "Mouse Problem" sketch from Episode 2, the address and phone number of an interview subject who has admitted to wanting to be a mouse are displayed and read out by John Cleese. In the original broadcast from 1969, the phone number was David Frost's home phone number, and after fielding a large number of prank calls, an annoyed Frost complained to the BBC, who edited the number out of the first re-runs in August 1970.
In the first run (1973), show no. 38 started with a Party Political Broadcast that was choreographed. Upon the syndication rights changing in 1983, the brainiacs at Time-Life (first syndicators) erased it. It was replaced with brief superimposed titles. The first DVD release of the Monty Python 16-Ton Megaset delivered an even worse blow: the previews of BBC comedies ("Dad's Pooves", "Up The Palace", etc.) at the end were left out.
Executive Meddling: If the episode with the Tudor porn shop seems disjointed, that's because it had to be edited rather severely before it was allowed to air.
The "Political Choreographers" sketch was edited out of one episode after its initial broadcast and apparently only survives in a low-quality off-air recording.
Additionally, most episodes of the two Python precursor series, Do Not Adjust Your Set and At Last the 1948 Show, have been wiped.
This could have happened to Flying Circus itself were it not for the actions of Terry Gilliam, who bought the masters as soon as he could.
There is an animated section in between the "Crackpot Religions" sketch and "How Not to Be Seen" involving Jesus and the two thieves being crucified on telephone poles, while an Alter Kocker Satan (played by Idle) appears out of the ground. It was cut after its initial showing, can only be seen in low-grade, black-and-white footage, but the image of the crucifixes can be found in a split second when the episode is "recapped" in fast forward later in the show.
Hey, It's That Guy!: Relatively few roles were played by anyone outside of the Pythons themselves, and were normally relegated to whenever they needed more than six men on screen at a time, and Carol Cleveland normally played the more buxom women.
However, the episode "Mr & Mrs Brian Norris' Ford Popular" closes with a fake talk show hosted by the "It's" Man. His guests are British singer Lulu and Ringo Starr. As themselves.
Also appearing as himself, Richard Baker, a well-known straight-laced news anchor of the BBC, who's rather confused about lemon curry.
Thames TV continuity announcer David Hamilton appeared as himself in Episode 39, which opens with the Thames TV logo and Hamilton declaring, "We've got an action-packed evening for you tonight on Thames. But right now, here's a rotten old BBC programme!"
In addition to collaborating as a writer on a few sketches, Douglas Adams appears briefly in at least two sketches, once as a surgeon. Incidentally, this appearance was on Episode 42.