At some point around in the early to mid 2000 era C Dory began to make a removable raised floor (the inner hull as bottom of bilge remains the same). Then about 2006-2007 there came a permeant raised floor, but occasionally water would get under this, so the problem could still remain.
In my 22's I had two bilge pumps. One aft in a sump between the tanks, to take care of water when the boat was in a bow up attitude (running over 5 knots approx) and one for lower speeds at the forward end of the cockpit or just inside of the cabin.
Most put some grid on the cockpit floor (inner hull) such as "dry deck"--we used that with heavy duty industrial foam pads on top.
Keep the cockpit covered when the boat is not in use. Use a full cover or cockpit slant back.
I would recommend that you do the same. I would raise the threshold, make a step or box, for a pump intake which would suck any water out of the forward part of the cockpit floor/cabin.
The plug under the platform probably was placed there either from water from the anchor locker (often improperly sealed, too high a drain hole), or from a loose screw and penetration from attachment for the brass strip which helps to protect the stem of the boat.
You will determine if any of these have to be addressed in the future.