In the cellar fight, Nigel Stock's hair changes from ginger to gray and becomes substantially longer and bushier when the stunt man is substituted.
Approximately 30 minutes into 'Do Not Forsake Me Oh My Darling' the rebodied Number Six walks into a Photographic Shop. On the door an advertisement poster is folded over twice at the top so as not to show the product name. A moment later Number Six looks back through the door and sees a man watching - the poster is now only folded once and advertises "The Polaroid Swinger".
In some of the car driving shots the actor is not Nigel Stock but looks to be McGoohan. This is particularly evident after he has left the camera shop and is returning back home, as the car makes a right hand turn. Likely due to using stock footage of McGoohan driving rather than filming Nigel Stock doing it.
Number Two: (as Number Six paces his flat) What sort of opinion would you form of that fellow?
The Colonel: Anybody who spends his time doing that must be rather stupid.
Number Two: You couldn't be more wrong. Because he's our most interesting citizen from every point of view... particularly yours.
Number Six: You're still as pompous as ever... Danvers.
Danvers: Where did you get my name?
Number Six: Jonathan Peregrine Danvers. Boorn in Bootle. Took elocution lessons. Came to London, joined the civil service in 1948 as a junior clerk, but moved to this department sometime later. Mainly at the request of the typing pool. Am I going to see Sir Charles? Well? Or would you prefer me to go on. I'm sure these gentlemen would be most intrigued to hear of your little jaunt to Paris in March 1958. Let me see now, what was her name...
Seltzman: If you really are who you say you are, you would not have expected me to keep it, would you?
Number Six: No. It's a hopeless situation.
Seltzman: If I had kept it, I would have been very stupid. Silly.
Number Six: You've made your point. I accept it.
Seltzman: But you overlooked one thing. Sentimental people are sometimes stupid. Very stupid.
Seltzman: I will do it... on certain conditions.
Number Two: I'm sure they will be reasonable.
Seltzman: For once, I am dictating.
Number Two: Heil.
Professor Seltzman would not have been able to identify Number Six by his hand-writing as he was comparing it with that on a letter mailed to him. Since he didn't actually witness the Prisoner write the letter, how could he be sure that it was actually written by him?
Henry Longhurst and Danvers Walker are credited but their scenes are cut from the final cut of the episode.
The address on the letter Number Six sent to Seltzman is "20 Portmeirion Road," an in-joke to the filming location of The Prisoner.
The episode opens non-traditionally, with a pre-credits teaser of Sir Charles and his men going over the photos. After the standard opening credits, the scene of Number Six waking up features different background music and no sequence of Number Six walking through the Village, running along the beach, or the standards "Who are you?/I am not a Number!" exchange between Number Six and Number Two.
This is the only episode in which someone other than Patrick McGoohan portrays Number Six. He is played by Nigel Stock here.
This is the only episode in which they both appear where Patrick McGoohan (Number Six) and Angelo Muscat (The Butler) do not share a scene.
This is the only episode of 'The Prisoner' in which Number Six touches a woman in an affectionate way, the woman being Number Six's fiancee. This is probably because the actor portraying Number Six is not Patrick McGoohan, who objected to doing scenes of this kind. This is probably why intimate scenes were written out of two other episodes which would have featured McGoohan, 'The Chimes Of Big Ben' and 'Many Happy Returns'.
The working title of this episode was "Face Unknown."
The footage of Sir Charles Portland's party is taken from "A. B. and C."
The footage of Number Six (Patrick McGoohan) pacing around his front room, eating toast and drinking tea, is taken from "Once Upon A Time" which, although it was aired after this episode, was actually filmed months before.
The final scene is the only one that Patrick McGoohan (Number Six) actually filmed for this episode as he was filming Ice Station Zebra in America at the time. All of the other footage of him is taken from other episodes. He also recorded several voice over lines for this episode.