Here - I've found one - it's not easy to see, but each of the Bowden cables controls a pair of points that operate simultaneously. The 'far' point travels to its extreme movement first, in either direction, and the kinks in the linking wires allow a little more movement in the 'near' points after the 'far' ones have 'made'. The cables came up through the edge of the baseboard to levers with high-friction pivots, to hold the 'near' points in place against the spring of the mechanism. Even with just home-made plywood cranks held in by a wood-screw, they worked almost faultlessly for years. It was only really a lash-up to see if it was worth doing properly, but it didn't seem to need improving, so it was never improved...