I could list a load of hills where there's no PROW or Access Land that people access regularly without any issue. The two nearest to me are Mynydd y Cwm and Mynydd Rhyd Ddu.
To, for your own access to the second one you commented on your blog
"The first objective was the lesser-spotted GW/NW-073 - Mynydd Rhyd Ddu. I had fully intended to follow BVE's described route, but Jimmy had been studying the map and wanted to "just check out" the line from the highest point in the road to the south. Surprisingly, there was a convenient parking spot right at this point, and the gate into the field was open. A fairly well trodden route ran from here to the summit, albeit with several fences and gates to be climbed. At the summit we were joined by several farm workers in tractors, JCBs and 4WDs. They had witnessed our approach to the summit and our radio gear, but did not come to talk to us. One of them did give us a wave goodbye as we made our way off the summit though!"
I've read the general rules and find no incompatibility with my view.
"All Expeditions must use legitimate access routes and comply with any local rules regarding use of the land. In particular, Activators must ensure that they have any necessary permission to operate from their chosen Summit, or that access is customary."
"Here checking access rights means checking websites, maps, notices in the nearest village or tourist centre as well as onsite footpath notices. Activating a summit where permission has not been given or implied by ‘open access’ will invalidate the activation."
If there's a reasonable route onto a site that I can see others have followed and no one has had any issues then customary access is established for me, even if there are some old signs dating from when the site was being worked with heavy machinery. If it's not fenced off then I treat it as "open access". The access roads in Jimmy's pictures are just that - access roads dating from when the tipping and subsequent landscaping work was being done. I certainly wouldn't expect to access by motor vehicle. Also, what if you come from the other side where the current summit lies?
Anyway, Gerald OIG will tell us all soon. If he gets up there without challenge or problem then I will treat that as "customary", if he has a problem then of course that is another matter.