most boats have wood stringers and transom until you get to the early 00's
guarantee that over 98% of fiberglass boats from the 90's were wood core
many high-end low-volume builders still use wood and balsa in various sections as core because its cheap.
production boats today have engineered stringer tubs glued together with plexus. while there is not the rot of the old wood structures, the glue joints fail after a while requiring that either you replace the boat every 15 years or you restore it.