Discrepancy in birth date

My paternal grandfather, Peter Julius Otto von Fircks, was born at Nurmhusen on 23 February 1876. At that time Nurmhusen, the Fircks family estate, was in Kurland, now Latvia. His name, date of birth and death, are recorded in the family tree composed by my cousin. My cousin was the family genealogist. He collected information like a magpie collects shiny objects. He has written several books about the family and collated quite a few editions of the family tree, including one which adds in the children of the daughters of the family.

To me, my grandfather is a fascinating character. I have heard anecdotally and from translating the journal written by my father’s eldest sister in German, recounting her history, various stories about him. In it she describes her father as “very handsome, 194cm tall, very slim with a large aquiline nose and very thin hands and feet. Even in the harshest of winters he refused to wear gloves and he was always reluctant to shake hands with anyone.”

In this photo, taken in 1920, he is 44 years old, but to me looks many years older. My father, the youngest of his children, was born in the previous year. The family had already lost their estate, fled their homeland and were experiencing poverty for the first time in their family’s history.

According to my aunt, my grandfather was a great reader. His interests lay in alternative medicine and anthroposophy. If he read anything else, it was most likely intellectual, as my aunt writes that her mother had to hide her romance novels from him. In his middle age he studied iridology and homeopathy, becoming an alternative practitioner. He met and was a follower of Dr Rudolf Steiner. He was a loner, very strict and not easy to live with. He demanded quiet and understood very little about children or indeed about anything practical.

However, my grandfather’s birth date in Ancestry doesn’t match our family tree. According to the Mecklenburg-Schwerin district of Germany Census in October 1919, he was born on 6 March 1876, not 23 February. I assume he would have completed the census himself, and that he knew his own birthday. Unless my cousin has it wrong, and my grandfather’s birthday is really 6 March.

My grandfather’s identification papers from the Germany Reich, stamped in 1940, confirm my grandfather’s birth date is 6 March 1876. And he is 189cm tall, about 5cm less than my aunt described him. Of course, he could have lost a few centimetres over time, or she could have guessed incorrectly. His occupation is listed as a Homeopath, so at least that matches.

Among my father’s possessions, now mine, are copies of the genealogical record of German nobility, the Gothaifches Genealogisches Taschenbuch. There my grandfather’s birth date is stated as 23 February 1876. Perhaps this is where my cousin got his information.

So, the mystery continues. Why would my grandfather have two different birth dates? Which is the correct one? How do I find out?