You need form them to calculate the plan-year earnings, so it seems that means "Check here if you want us to calculate Plan Year and applicable GAP_Period earnings for this and all future Corrective Distributions" that you need to mark the box. I read it as your instruction to have them calculate both or neither. Since the distribution should happen before the gap period, marking the box would result in this case having them calculate just plan-year earnings attributable to the excess contribution, which needs to happen.
