The first Lib split had no inserts but was also not designed to be direct mounted like a ski. That board still had to have inserts installed before use. In order for a board to be mounted like a ski the core would have to be thicker and reinforced to the point of altering the ride of the board.
I raced on boards in the early days that were still mounted ski style. Nothing ruins your day faster than pulling your binding completely out of the board mid carve. I ended up t-nutting most of my boards in the days before 4-hole.