Regarding the beveled edge, My own experience is that they are not very common and the only pieces I have personally observed them on are newer. I would also add that I am referring to non geometric pieces. I venture to say that you guys across the pond see a much greater variety of this type of glass than I do in Seattle.... so my experience may simply be limited by geography.....
They have always struck me as a portion of work that was done to clean up something unwanted. On a piece such as this with an organic form and completely curvilinear lines, it seems a geometric detail which in the whole design of the piece is out of place. None of the pieces I have with curvilinear lines and ground bottoms have a beveled bottom edge on them, but all of the geometric pieces do.
Craig