How to setup pending action to trigger only for newly added dependents and suspend only the new dep

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Our requirement is that when a new dependent is added with New hire /Child Birth or Marriage, documents should be provided and verified within 15 days of the event. We are using a action item due date formaula for this. For ongoing event or dependents, there is no due date

My designation level is 'Plan Type in Program' and currently i have setup designation and certification at the PTIP level for specific life events like New Hire, Marriage, Child Birth etc. I do not have any certification or designation setup at plan/OIPL levels. The issue i am running into is