And alternative to starting in Bilbao is to start the Olvidado in Pamplona. I think @caminka and @Sheffield James have walked this variant, or parts of it. This guide indicates stages and routes, but notes that it is not (yet) waymarked. I would not be surprised to see more promotion of this route.
In fact, I think it’s @caminka’s guide that is posted in a pdf on the site! http://www.viejocaminoolvidado.com/.../12/4.-Camino-description-VIEJO-public-13.pdf
Ruta Pamplonesa del Camino Olvidado, el Viejo Camino de Santiago
Descubre el itinerario completo de la ruta Pamplonesa del Camino Olvidado. Descubre lugares por donde pasar, alojarse, rutas...
In fact, I think it’s @caminka’s guide that is posted in a pdf on the site! http://www.viejocaminoolvidado.com/.../12/4.-Camino-description-VIEJO-public-13.pdf