Facebook birthday sync only working for some contacts I recently noticed that only a couple of my contacts' birthdays show up on my calendar on OS X.  For instance, I have four friends with birthdays today, but only one is on my calendar.  I tried deleting and re-adding my Facebook account but notice no difference.

I'm getting the exact same behavior on my iPhone.  

Maybe this isn't a Mac issue.  Did Facebook change the way its sync works?
Facebook has an option for friends to Opt OUT of their birthdays being displayed to other people. So if I had you on FaceBook and I turned the option off to display to you what my Birthday is, the it won't sync to your Calendar.