then that is a fault of the renderers and the renderers should be the one to fix it. It is bad practice to tag for a particular renderer, please see: https://wiki.openstreetmap.org/wiki/Tagging_for_the_renderer
NCN routes very regularly follow roads, this is not a rare case and it being a service road doesn't change anything and ncn routes should be tagged with bicycle=yes or bicycle=designated and also have a route relation.
