That doesnt matter for the lanes tag, please see the wiki article (https://wiki.openstreetmap.org/wiki/Key:lanes) where it says "Note that it is valid to tag lanes count also in case where lanes are not marked with paint on the surface"

The correct way to tag roads with no lane markings is the lane_markings=no tag (https://wiki.openstreetmap.org/wiki/Key:lane_markings)