Roy, it was in my mind somewhere that there had been other Robinson & Bolton pieces shown on GMB, and I had done a search on GMB but got no result (?), so thank you for the link.
So now we only need RDs 187536, 189615 and 189616....
From the various photos, the quality of the Robinson and Bolton pressings looks first rate, and it may be that there could be several different shapes for a given design.