Ludwig van Beethoven 

Although his exact date of birth is uncertain, Beethoven was baptized on December 17, 1770.

Since as a matter of law and custom, babies were baptized within 24 hours of birth, December 16 is his most likely birthdate. However, Beethoven himself mistakenly believed that he was born two years later, in 1772, and he stubbornly insisted on the incorrect date even when presented with official papers that proved beyond any reasonable doubt that 1770 was his true birth year.