Sorry I hadn't commented on this thread for a while. I've been on 'stormy seas' lately-
The marlin spike used to untie knots is, of course, a fact and indeed I think these stylus types could have seen sea service. Much as fids were used for very thick rope, I feel the small spikes could have been effective with smaller lines and also would have been a great tool for punching holes in sailcloth or other fabrics, etching scrimshaw, etc.