Can you give an example of such a road, maybe post 2 endpoints we can enter into mapsonus and see such a route?

Yes, California State Highway 49 and California State Highway 20.

Example start and end directions:

National Hotel
211 Broad St
Nevada City, CA 95959

Shell Station
16978 Penn Valley Dr
Penn Valley, Ca 95946

Using those two addresses in popular search engines, you get...

MapsOnUs names significant sections of 49 and 20 as "unnamed road".

MapBlast is the simplest, giving only two directions. However it doesn't specify that you need to turn onto 20 at one point. See, when you start the journey, you are on a single stretch of highway that doubles as 20 and 49 together for a while. Later, they split off into separate 49/20 highways. Mapblast doesn't tell you about the split. Although it is accurate for it to just say "take highway 20", you might miss the turn if not directed to do so.

Mapquest is the most accurate, giving dead-on precise directions of each turn.