All of the JCs are cored. Mine was one of the very few done in solid glass. On the older JCs I have not heard of any horror stories of coring problems. On my 84 I was amazed at how well the coring on the decks and hardtop was when I install some new hatchs.
On the early JCs before the coring goes in JC placed solid glass mounting blocks into the hull. The blocks were in areas such as the rudder posts, water intakes, & transducer pods areas. Some JC were cored above & below some just above.
I would carefully inspect all areas where spray rails, 1/4 quards & both above & below deck thru hulls are. Pulling a few is also a good idea. When looking at the above water line thru hulls if they are plastic and have cracks that could be an indcation of water which may have frozen at one time.
To JCs credit and all areas where the coring exposed, JC always did a masterfull job at protecting it.
It is the areas that others have exposed over these 30 + period that could lead to troubles.
Lastly on some of the real old JCs the tanks were made of steel. They were very heavy & rust never sleeps. I believe they switched to fiberglass in the very early 1980s.
Mine is a 91 cored and dry thankgod. when i went to purchase the boat i had my surveyor do a thorough job on looking for moisture. This year i just replaced all through hulls and took the extra time digging out the coring aound the hole and refilling them with glass and resin , so in the case if the 5200 did let go and leak that the hull would not get saturated.
like everything else, things have there pro's and cons.