A few years back was watching one of those fishing shows, where some old guy and crew were fishing for tuna (not the new drama shows) old school, real fishing. He whipped out a knife to gut a fish and a massive 12 inch coticule. Slapped the yellow side on the hatch and sharpened the knife on the dark purple/ BBW, then tossed the stone into a wooden box like it was a rusty old hammer, never even looked at the yellow “backer”.
Makes perfect sense, my BBWs leave a keener edge on any tool in comparison to my Coticules.