While Mickey's birthday was always linked with his public debut in Steamboat Willie, it was actually celebrated on different dates prior to the 1970s. Due to errors on the studio's early press releases, Mickey's fifth birthday was celebrated on September 30th of 1933, his seventh was celebrated on September 28th of 1935, and his tenth was celebrated on September 27th of 1938. And in 1968, his fortieth birthday was celebrated on October 28th. It was not until the early 1970s that it was officially confirmed that Steamboat Willie's original release date in 1928, and Mickey's official birthday, was November 18th.
Disney has officially stated November 18th is also Minnie Mouse's birthday, due to her having debuted alongside Mickey in Steamboat Willie. However, this does not seem to be the case in fiction; numerous productions that take place on Minnie's birthday do not mention it also being Mickey's birthday, and vice-versa.
In the Chip 'n Dale Rescue Rangers comic story "Cobra Kadabra", Snout mentions that he is a Pisces, which would put his birthday between February 19th and March 20th.
In the Recess episode "Outcast Ashley", Ashley Quinlan states that she is a Leo, thus revealing that her birthday is between July 22nd and August 22nd. In the same episode, Ashley Armbruster states that she is a Gemini, which indicates that her birthday is between May 20th and June 21st.
In the Mickey Mouse Works short "Whitewater Donald", Daisy Duck mentions that it is Valentine's Day and also her half-birthday. This would indicate that Daisy's birthday is in the middle of August. However, in the short comic story "Forget Me Not", Daisy's birthday is given as December 1st.
At the end of the Teamo Supremo episode "Will You Be My Valentine Bandit?", the Birthday Bandit asks Skate Lad, "Isn't your birthday in about a month or so?" This indicates that Skate Lad's birthday is in the middle of March.
In the Kim Possible episode "The Ron Factor", Ron mentions that he is a Virgo ("Dude, I am Virgo, but what's your name?"), which would put his birthday between August 22nd and September 22nd. However, in the later "Trading Faces", he says "I'm surprisingly nimble for an Aries," which would indicate his birthday is between March 20th and April 19th.
In addition, according to the 104 Days of Summer! board game, Baljeet Tjinder's birthday is said to take place on the 13th day of summer vacation. Though this does not give a specific date, it does imply that Baljeet's birthday is in June.
Also, Perry the Platypus has a birthday in the comic "Happy Birthday, Perry!"; thus, his birthday is likely also between these dates.
Conflicting with Major Monogram's birthday being celebrated in the summer in "Backyard Hodge Podge", he mentions in "Operation Crumb Cake" that he is a Sagittarius, which would mean his birthday is between November 22nd and December 22nd.
In the Toy Story comic "The Return of Buzz Lightyear", Andy Davis receives a surprise gift from his grandmother during August, and his toys are surprised about this because Andy's birthday is not in August.
Kermit the Frog's birthday
While it is well known that Kermit the Frog was born in a swamp, the precise date of his birth is uncertain, with different months and days specified over the years (though it is unanimously agreed upon that he was born in 1955, the year he was created).
The earliest reference to Kermit's birthday came in an appearance on Dinah!, hosted by Dinah Shore on April 13, 1977. In that episode, Kermit celebrated his 21st birthday. As Karen Falk noted in an "Ask Henson" column circa 1999, "Kermit first appeared on television in 1955 (so he would have been 22 in 1977, but many show business people fudge their ages a bit!)." Falk also added that "the official year is 1955, but there is no official date. Besides - do you count when the egg was laid or when the tadpole lost his tail?"
In episode 406 of The Muppet Show, which was taped in May 1979 and aired in September of that year, Miss Piggy arranges a birthday tribute show for Kermit. However, the frog claims that his birthday is "about four months" away.
In 2005, with the 50th anniversary of Kermit's "birth," the issue of assigning a specific date resurfaced. A National Public Radio Morning Edition report, broadcast on May 9, claimed that Kermit was born on that day; the actual broadcast focused on Kermit's "birth" as a puppet creation as opposed to an actual celebrity, and chose May 9 since that was the date Sam and Friends debuted. The date was repeated on Wikipedia, in personal blogs, and other materials in 2005. However, most print news periodicals referred to "Kermit's birthday" only in terms of years. In contrast, MSNBC, in an August 21, 2005 article, claimed that Kermit would turn 50 "next month," possibly alluding to Jim Henson's own birthdate of September 24th.
In 2006, the May 9th date cropped up again, in a Ford press release promoting the debut of Kermit's Ford commercial during the Super Bowl on February 6, 2006. The press release, which treated Kermit not as a puppet but as genuine "celebrated actor, author, singer and journalist," included a biography of Kermit, which gave his birth date as May 9, 1955. However, when Kermit guest starred on Martha on October 5, 2006, the guest profile on the show's website insisted that Kermit was "'born' on May 9, 1955, in the mind of puppeteer Jim Henson," as opposed to a literal birth date.
In his book Sesame Street Unpaved, David Borgenicht gave Kermit's birthday as February 29th, Leap Year Day. Since this is the only mention of this date, this could be interpreted as a joke about frogs leaping, and not as Kermit's official birthday.
In episode 106 of The Muppet Show, when Kermit and Jim Nabors discuss astrological signs during the talk spot, Kermit claims to be a Taurus, which would make his birthday between April 20 and May 20. While that's obviously a coincidence, it does give credence to May 9th as Kermit's birthday.