Difference in date of birth

[Rinkle soni]

Dear Sir

I am under MPNP process and need to prove sibling relationship between my mother and my aunt. The DOB of my mother is 10.12.1969. But my aunt while she submitted her details with CIC (At the time of her PR in 2015) gave my mother's DOB as 10.12.1967. The name of parents on all the documents is the same.
Please advise on DOB issue and oblige.