Well, I think there still needs to be something that completely cleans and rebuilds the birthdays (not the events).
This would cover all bases so we wouldn't have birthdays showing for deleted or banned members - that is unless you are going to add a "Remove Birthday" routine when banning or deleting.
If you can't make sure that there won't be an orphaned birthday out there with no way of knowing, then you need something that can clean and rebuild based on the "Allow others to see my birth date?" check in their profile.
The lack of tools for the calendar has been especially frustrating. You need to start offering some useful ones.
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