I (or another staff member) usually just hand out the emblem when I see a new birthday thread in Celebrations. The reason why it's not done automatically is because it'd be, tbh, a load of hassle going through everyone who has a birthday on one day and handing out the emblems. But I guess we could remove the birthday thread requirement part and make it requestable through here like the Veteran one. I kinda like it the way it is now, though.
That said it's not a 100% set emblem. I think it's been handed out before to people with threads so idk exactly what's happening here, but at least that's how I normally do it.