The M52 has fascinated me for some time (I even built a crude FS5 model of it). I think there was a C4 program entirely on that subject a couple of years ago, with much the same footage as the J. Clarkson program.
Even though the evidence is compelling that the M52 incorporated the all-flying tailplane long before Bell 'invented' it, I doubt Chuck or any other US authority is likely to accept it publicly. I suppose it is possible Bell arrived at the same solution independently without benefit of the Miles data? The answer lies in the Bell archives
I wonder what the Smithsonian have to say about it?