Today is my grandmother's 95th birthday, but she does not remember that it is today. She believes that it is tomorrow because all of her life she and her family celebrated on the 15th. We guess that the lie originated with her parents who used the date landlords are required, by law, to turn on the heat for tenants as a memory device to earmark her pseudo birthday. After all, she was one of eight.
We found this out a few years ago because she needed a copy of her birth certificate for some reason or other and on the certificate, the date, in all of its glory, revealed the falsehood, shattering our world. Well, not quite, but it was pretty weird.
Happy 95th, Grandma.