Old Coach Road Relevance and History

I wonder if anyone can give me any idea as to the relevance and importance of the Old Coach Road, which runs eastwards along the top of the Hampden Range on the Nullarbor.

Whilst filming along the Trans Line recently, I was fortunate to speak with local historian, Jill Campbell from Kybo Station. Researching the next part of our story, I asked her about the Old Coach Road, and she told me that she had never seen evidence that the road was ever used as a regular route.
I subsequently purchased a copy of a book called “The Overlanders - Crossing the Nullarbor - 1870s-1970s”, which is a 300 page A4 collation of newspaper items and travellers own stories from the period.

There is no account that indicates that anyone took that road. With the advent of the Overland Telegraph Line, travellers either followed the original line from Esperance and Israelite Bay, or travelled via Frazer Range and the new Balladonia Telegraph Station to Madura Pass, where they descended to Madura Station, then followed the Telegraph Line along the bottom of the scarp to Mundrabilla Station before reaching Eucla.

The Eyre Hwy was built in 1942 following that same course.

So the question is, what is the relevance of The Old Coach Road, and have Hema got it wrong with their mapping description?