I think the D509 type of issue is just a trade off. At least when in happens in the US: It is the "official" designation and can be used on Post, while the local name changes from town to town. That is less of an issue when navigating within the same town, more of an issue when navigating through towns: Go 30 miles along a "CR" county road and it might change names 4 times. Rather confusing for directions to make it look like you have to travel down 4 different roads for that one leg of the journey. I suppose Google could show both though, depending on zoom level.