Part of the whole point behind mapping everywhere the vehicles go is so they can mark ahead of time the locations of signage and lights, lane markings etc. Now whether there's a bunch of Vehicle to infrastructure sensors all over the place, or carefully curated internal maps, there will inevitably still be unmarked changes in road conditions, so Robotaxis will still need to be able to recognize changing signage and lane markings, along with all the other dynamic elements on the road.