Ferricyanide in this particular case would have had the disadvantage of bleeding out in the black area next to the boards, lightening the dmax and turning its color somewhat. In practice that tends to look rather yuck.
Not if it's done well, but you need to be precise & persistent. The ideal print is often softer and more heavily burned in than people might think - and warmer toned papers respond better (or at least have less propensity to take-off and stain if not watched like a hawk).