The "floor" of the hollow coaming is the "ceiling" of the Q-berth liner. Some kind of access hole has to be cut into this in order to service the winches and other hardware installed on the starboard coaming. They were apparently installed at the factory before the deck was joined to the hull. Sounds like a storage nook may have been the solution on your boat. Mine has a deck plate in the Q-berth side that you have to reach up into from below.
Water that gets in there would drain into the "duct" that runs along the hull-deck joint and then drip into the aft lazarette space at the back of the cockpit and eventually to the bilge. However, due the curvature of the boat, and whatever the workers did with the ends of the fiberglass sheets at the end of the piece, the "duct" does not drain freely on my boat and water pools up in it, and spills over behind the plywood panels, across the "shelf" and down onto the Q-berth mattress.