Yes, the anecdotal evidence suggest that the amine hardener, as well as some creative "stuff" used in production of the hardener in the early days of epoxy resin production, cause the reaction. Additional evidence points to acetone as the carrier compound that helps the hardener solution penetrate skin membranes. I strongly suspect that, a lot of these cases were a consequence of epoxy users "bathing" in acetone washes to compensate for the fast evaporation rate due to its low BP,but obviously there is no way to stratify volume of acetone use per worker or shop with frequency of contact dermatitis retrospectively.
Over your thirty-five years of boat building, I am sure you are also aware that formulations of hardener have evolved to employ amine compounds that are "cleaner" and potentially offer lower hypersensitivity rates on chronic exposure.