I've now given away my one piece of Bristol Blue - but looking at my pic on the Glass Gallery it had a shallow kick and a snapped pontil scar.
Obviously it looks as though I mis-interpreted the picture showing the base of this decanter ..... thanks to Lustrousstone for the explanation of the 'four prong pontil rod'.

Looking again at that picture of the base it would seem there isn't any final finishing i.e. grinding or polishing - just snapped from the attachment of those four marks - would that be correct Roy?