Rules not marking all registrations to complete when commerce order is complete
Have you experienced the issue with the failed card? I run an event website with entity registration and commerce and we process an average of 20 registrations a day and haven't had that problem yet. 

But if you want to be certain you could utilize hook_commerce_checkout_complete, look at the order payment details and check that the order has been marked paid successfully. If so, invoke the rule or use entity query to lookup all registrations related to the order_id and mark them complete.