First, you're shopping in the wrong place. Building centers are great, but they don't normally sell many low volume items. Go to a real lumberyard. Not all plans call out marine plywood. Marine is important when the plywood will be bent.
Marine plywood has no voids running across the panel, exterior does.
If the bend is particularly pronounced at this point or there is a lot of stress, it could fracture at the void. That's your call. If the boat you intend to build is a high speed boat that will take a lot of pounding, do you want to take the chance. Put the best sheets in the forward sections. If you have a choice, use marine if called for.