Mystery Monday: Forgotten Age???

The grandpa that my grandpa remembers best and talks about most is his Grampa Tony.  I was told it was short for Anthony William Konst, but in reality he was born Anton Wilhelm Kunst.  In agreement is that he was born to Henry Kunst and Anna Kramer in Burlington, Racine County, Wisconsin on March 3. I have the family history my great grandmother, Tony’s daughter, wrote down in her own handwriting while she was sitting with her parents.  I have a photo of Tony’s grave stone.  Everything lists his year of birth as 1867. 

However, the baptism records clearly show his year of birth as 1868.  Clearly.  And this is the record made closest to the time, so one that I must believe the most.  So WHY?  I don’t see how it could be a mistake.  His parents were married in January 1867 and he was actually born a year and two months later, but they tell everyone he was born two months after they were married?  That seems backward.  And that there is a story that is missing.