One day late (on my side), this just in from Dennis Books:
["HAPPY BIRTHDAY TO MICKEY MOUSE ON HIS BIRTHDATE OCT. 1st "
Perhaps this date will cause controversy ? I have Disney Studio records showing that throughout the years Mickey's birthdate has been celebrated on various days in September and October. HOWEVER I recently found a letter written by Walt Disney in which he stated "He was born on Oct. 1, 1928. That was the date on which his first picture was started so we have allowed him to claim this day as his birthday". I guess I will have to go along with Mickey's father.]
Of course, today Mickey's official birth day is recognized by The Walt Disney Company as November 18, the day of Mickey's screen debut.