"I also remember reading that Uffington has changed over the years - or is that somewhere else?"

I don't know, but I'd previously wondered if there's a natural tendency for successive re-cuttings to cause the thing to morph thinner, as people fail to cut back the encroached edges as far as they should. It looks as if they could have kept true to the upper lines but allowed the grass to encroach on the lower ones.