The official "Eurovelo1" / "Nasjonal sykkelveg 1" route seems to continu southwards along Namsosvegen. I have not been able to find any reference to the route chosen between the Namsosvegen/Osenvegen intersection and Trondheim.

The official route is digitized in this gpx: https://en.eurovelo.com/route/get-gpx/2?developed=1