Is it possible mum was everyones "calendar"? I know if I don't remind my brother of birthdays outside his immediate family, they wouldn't be acknowledged at all...
I can't rule out that she wasn't the calendar of the family, I know she certainly was for my dad and brother, but the aunts and uncles she never really spoke to too much - she was always shy on the phone, or rather, too busy to stop and chat to most people...