I'm using the next system
If I have a sum of subtasks, I don't assign any date information on a main task. Instead of it, I assign to it a custom status "Designes (or Planned): Laid aside". It means that this main task won't be available for viewing in My Work (no any encumbrances in there). Also it means that only when all subtasks with assgined dates would be have statuses "Archive: Completed" or "Archive: Cancelled", this main task could be turn into "Archive: Completed" too
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