1) A highly unusual situation, but it's not hard to have the policy defined so if AC+ was already purchased prior to activation and there was an accident the date should be adjusted to the date of purchase.
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Oh, so now you want to bake your own cake and eat it too. No insurance company in the world would allow the policy to be backdated only if an incident takes place before the policy start date. It can only be one or the other, and I dont think the risk is that low either. That phone could still be at risk sitting under the x-mas tree still in the box. Your scenario is the same as me paying an insurance company for life insurance with my policy coverage effective only from when I start my job for a security firm in Syria, yet then dying on the plane to Syria and then asking the Insurance Company to backdate the policy as I died after I purchased the policy but before it became effective.