I have not found any recent reports of a through trip from the Golden Valley end to the Butterley Wharf, are there any?, this would answer your query, similarly, has anyone been in the other end (West) since they put in the A38?
Other things that seem to have been forgotten by the heritage people are the Codnor works and the Pinxton branch, as a sprog I walked every inch of the the towpath from Cromford to Langley Mill, including the Pinxton branch.
The map seems to put the tunnel quite a way from Butterley Reservoir, a feeder for the cut, suggesting a sophisticated water management system?
I recently went on a sentimental journey to try to locate points west of the tunnel and got awfully confused, it made me determined to sort out my pictures of the triple bridge at Lower Hartsay (sp?), Kodak Browny 127, B&W, not found them yet but still looking. Watch this space!.
Always remember, nature is in charge, get it wrong and it is you who suffers!.