Bertha's birthday!!

It was with great excitement today that I realised the importance of the date...26th January, 2009. No, not because it is Australia Day, or because it is my 24th wedding anniversary, but because, according to Bertha Hughan's official birth certificate, it is her 170th birthday today!!!
I certainly wasn't aware, when I was sweltering through a scorching Australia Day wedding at Yarrawonga in 1985, that it was my great-great grandmother's birthday. And even now, the 26th of January is just one of three dates that I have for Bertha's birthday.
Her birth certificate states that she was born on "Twenty sixth of January, 1839'. The admittance form of her brother Allan to attend the Royal Caledonian School in 1844 gives Bertha's date of birth as January 19, 1839. And, finally, the birthday books of three members of Bertha's family all have her birthday as being January 1st, and in two cases the entry was in the handwriting of Bertha herself.
Of course when presented with three birth dates from three different sources, I have to accept the one which is an official document...in this case, her birth certificate.
As a young women, Bertha decided to take two years from her actual age, and from that moment on always gave her year of birth as 1841. I have a feeling this decision came as the result of her falling in love, at the age of 22, with a young man of 20...a whole two years younger than her! I feel quite sure that Henry Bishop, her future husband,did not know of this ruse...it was a little well-kept secret between Bertha, her immediate family and now, more than a century and a half later, us!!!
I have no idea, however, as to why she would change the actual day of her birth from the 26th of January to the 1st of January.