I found out why some of the birthdays are visible on the homepage and others are not. If you don't display your age in your profile, the only one that can see the birthdays is me using this id. Members can't see it. If you would like everyone to see that it is your birthday, select yes to show your age in your profile and it will show your birthday on the homepage but not your age. This explains why I missed a few of the birthdays during the past year as I don't log in that much with this id, only using it most of the time when I see a new member wanting to be activated. Sorry if I missed any birthdays over the past year.