A character with whom Madeline gets Ship Tease with originated with the unseen secret admirer Herman in Four Color Comics #796, titled "Madeline and Genevieve" in 1942. Pepito did not appear in the franchise until 1956.
Lord Cucuface's name being changed to Lord Covington in the 1998 film was preceded by the Shirley Temple's Storybook episode in 1960 which changed his name to Mr. Murgittroyd. Likewise the idea of a Setting Update also originates with that episode, setting it in the then present day if the mention of Frankie Avalon and television is any indication. The Adaptational Heroism for the Gypsies in the animated special of "Madeline and the Gypsies" also originates from this episode.
Viewer Gender Confusion: Pepito is male, but the books and DiC animated series give him a more feminine appearance, with hair just as long as Madeline's. The film averts this.
Writers Cannot Do Math: Due to a constant stream of retcons over several media, if you count the amount of named friends that attend school with Madeline, there are more than 12 girls. The only way it makes sense is if we view each installment where the girls have different names as Alternate Continuities.
Narm: "Lord Cucuface, beware! Genevive, noblest dog in all of France, you shall have your ven-ge-ance!" For the record, that line did not appear in the TV special. The movie did include the second sentence, albeit with a normal pronunciation of "vengeance."
Adaptation Displacement: There was a 1950's short, too. It's vaguely remembered, though it was put on the DVD release of the 1998 film.
In the books and early specials, Madeline's parents are known to be alive, and even appeared in the Christmas special. The live-action film, in which she's an orphan, caused DiC to retcon her into an orphan, much to the confusion of many. Although to be fair, only in Lost in Paris was she vividly portrayed as an orphan not unlike the live-action film, while the animated series after the movie does little to nothing about referencing that.
All Animation Is Disney: DiC was with Disney at the time the series and Lost in Paris was created, which made many people believe that the Madeline TV series and first Direct to Video movie were from Disney (It doesn't help that Lost in Paris, at least the original 1999 release before it was rereleased on DVD by Shout! Factory, opens with the text "Disney Presents")
Awesome Music: Long Live The King Of Chocolate. It isn't Aesop-y like most of the songs and is very catchy.
Fridge Brilliance: In The Movie, someone claiming to be Madeline's relative from Austria brings suspicion to Madeline because he trips on a suitcase and says "Sacre bleu!". It seems weird, considering that Translation Convention is in play and they would already be speaking French to one another... but then you realise that he is saying it in a french accent - it's not the fact that he temporarily spoke in French that made Madeline suspicious, it was the Ooh, Me Accent's Slipping.
Fridge Horror: The last act of "My Fair Madeline" up until Emma tells the King of England the truth about Madeline's role in the heist is full of this in regards to Miss Cleval, Lord Cucuface, and potentially France in general. As far as the King knew, this French nun who ran a boarding house and the politician who bankrolls her knowingly brought a thief into his country with the backing of the French government, and said thief very nearly steals the Crown Jewels after being caught trespassing in the palace and "assaulting" one of the royal guards. At best, if Emma had not confessed, then the King could have demanded Miss Clavel and potentially the French government as a whole to pay steep reparations for Madeline's "crime". At worse, he could have considered it an act of war.
Harsher in Hindsight: Lost in Paris, a story about Madeline being forced to work in a sweatshop, becomes this after the 2007 abduction and possible murder of Madeleine McCann.
And In-Universe example in the movie: when Uncle Horst brings the girls lace collars as gifts, it seems like a sweet sentiment from a relative who just met his niece just now. ...And then later in the movie, you learn about the Lace Factory, and all those orphaned girls who slaved to make them.
CINAR came up with the initial ideas for the specials and partnered with DiC to execute it. Then Cinar went their way when the partnership ended while DiC went on to make the the TV series and two specials. Almost two decades later, CINAR became Cookie Jar and subsequently bought DiC, and then merged.
One episode of the series is titled "Madeline and the Hunchback of Notre Dame," in which Madeline, Pepito and the girls perform a play based on Victor Hugo's novel. A year later, Disney released their adaptation of ''Hunchback'', followed in 2002 by a direct-to-video sequel which gave Quasimodo a love interest named... Madellaine.
Moe: Moreso with the animated series than anything else.
Then there's Pepito in "Madeline and the Bad Hat", who before he came around is gifted with a tool chest by Miss Clavel, which he uses to build himself a guillotine. With this, he beheads his chickens to cook for dinner. The girls and Miss Clavel react to this sight about as well as you'd expect.