I have a 1978 Mainship, it has a similar flybridge that extends to form a roof over the cockpit. I suspected there was moisture, even though there are no soft spots. Realistically, any boat that old with plywood core fiberglass is going to have some intrusion. So one day last year I drilled a hole up into the ceiling but not all the way through. As I expected there was some dampness. I believe I caught it in time, before rotting set in to cause any soft spots. So I decided to ventilate the core and drilled a few holes, 1 inch diameter into the ceiling, in various places. Some were bone dry, some showed moisture. A year later I occasionally check the holes for moisture in the core and there is none.
I don't believe wood should be fully encased, and I recall from Chapman's that it's bad to paint all sides of wood since it needs some places to allow the moisture to escape. I pushed little aluminum louvered vent caps into holes and they look fine. I think it should be standard practice to provide ventilation to wooden cores.
It's simply impossible to keep all moisture out of the plywood for decades, especially with surfaces that expand in the sun or flex under stress. I suppose it's possible if the lamination is perfect and there are no screws or fasteners but that's not feasible either.
I hope my next boat has full synthetic cores.