Birthdays repeat every year and do not need to be marked completed. The birthday remains a date on your calendar.
Yearly birthdays and occasions can have related tasks such as Buy a gift, Send a card or Send a message. Those tasks stay linked to the occasion. Their due date is recalculated from each year's occasion, so an option such as 1 week before remains exactly seven days before across leap years and year boundaries.
You can move or edit one year's preparation task without changing the normal annual rule. The one-year exception keeps its discussion and its Done/Skipped status. If its date is already in the past and it has not been done or skipped, it remains Missed.
If you add a preparation task after this year's calculated due date has already passed, Organise You asks you what to do: keep the past date for this birthday, make this year's task due today, or start from next year. It does not silently move the task into another year.
The birthday card shows whether that year's task is Done, Skipped or Missed. If an exception changes only wording rather than its date, Organise You describes it as edited for this year rather than moved.
If you temporarily delete the parent birthday or occasion, its preparation task can remain visible while the parent waits in the Rubbish Bin. The task explains this and reconnects when the parent is restored.
If you correct the birthday or occasion date for the whole series, the matching preparation-task dates, Done/Skipped state and occurrence discussions follow the recalculated dates. The same continuity applies when you correct a linked birthday from the Address Book, including any year you previously deleted or replaced with a one-year move. If you use This and future occurrences, future preparation tasks follow the new future birthday series while earlier history stays with the earlier series.
If you choose This occurrence only on the birthday or occasion itself, Organise You creates a one-year exception only. It does not create a second yearly birthday. Preparation work for that year follows the exception while later years continue on the normal series. If you edit that saved exception again later, it remains one year only and its calculated preparation task follows the new exception date. You can also add a new related task directly from the one-year exception; that new task applies only to that occurrence and does not repeat in later years. If you manually move that task away from its calculated preparation date, Organise You labels it as moved and still shows the normal relative rule for context.
Open a contact's View next calendar birthday link when planning ahead; the original date of birth remains visible in the Address Book.