I applied some close scrutiny to the "monolith extraction point" at Rhosyfelin on my last visit -- referred to by Mike Parker Pearson and colleagues as located in a "recess." There isn't any recess there, and there is no evidence at all that a single stone might have been taken from the point at which MPP has charmingly posed for a thousand photographs.
As I have pointed out before, the rock face here has several prominent fracture scars which must have been created when small slabs of foliated rhyolite fell away and accumulated at different times at the foot of the crag. If they were present in 2011, these must all subsequently have been carted away and dumped by the archaeologists, who were interested above all else in the 5 years of digs in looking for monoliths capable of being carted off to Stonehenge or to "proto-Stonehenge". It's possible, of course, that some of the slabs broke away while the site was affected by glacier ice and torrents of meltwater; they may have been incorporated into overriding ice, or moved downstream before being dumped. They must all have been quite small, and easily modified or destroyed.
The sample that was taken away for cosmogenic exposure dating about 3 years ago must have come from somewhere on this face. The dating must have been completed long since -- I wonder why the result has never been published? But then nobody likes to publish inconvenient evidence, do they?