It's something I've argued about with various people, including authorities, fairly often through the years. The Byway is bounded by fences .. just 'cos there's a stone track doesn't mean the stone track edges are the edges of the Byway. Do you think geese or cattle stuck to the single track on Drovers roads etc?
It's like the bombhole at Strata .. the track goes through the bombhole, but there's a 'safer' track round it .. which is the correct track? Answer is they both are .. and anywhere between the forest fence and the field fence at the other side!!
OK, it might look an eyesore if someone does tear the grass up, but it's not illegal when the track has properly fenced/walled/marked boundaries.
In my view, but this hasn't been argued yet .. the same could be said of Chapel Gate and Roych Clough .. there are parts, like the steps, where everyone keeps to the single track .. but it's possible to travel off this main track and go to the sides, right up to the fences .. how do we know this isn't legal? I doubt it's ever been tested in a legal sense. Walkers will say it's illegal, I've no doubt the Peak Park Authority would say the same, but it'd really need testing in court, or someone with some searching/legal clout to find a precedent maybe .. or the balls to go to the edges and get taken to court to prove where the boundaries lie ..
Same with 'normal' roads .. boundaries of the road are between kerbs but it's only convention and Highway code/law that we travel in the left lane .. there's nothing to stop us using the other lanes for overtaking though .. why not the same on byways like this?