Krogen stopped coring below the waterline in 1993. Before then, the core material owas pvc. Not perfect but better than balsa. There have been reports of some delaminate with the cored hulls however itís easy to detect during a survey.
We we sold our 1987 KK42 in 2021. We had no issues with delamination or moisture in the core. As part of the survey, the hull was thermally imaged. We did have a small area above the water that had moisture by a sink drain that was not bedded correctly from day one but that was it.