A number of videos of the Olympic North Coast and South Coast Routes can be found on YouTube to see what the conditions are like. As far as I can tell there are no markers along the beach and rocky shore sections. One of the videos I watched explains that the overland trails between shoreline sections are marked with signs like this and can be a bit hard to find sometimes:
As for what even makes it a route, I suppose we could ask the US National Park Service since they publish a fair amount of information about each one. If pages like that were published by www.wildjimshikingworld.net, I’d be inclined to say these are just some hiking routes old wild Jim recommends, and they are not qualified for inclusion in OSM. But when the documentation is coming from the land manager it feels a bit different.