One thing you might give a try, is to illuminate the pieces under long
and/or shortwave ultraviolet light. Certain types of artifacts, though
characterized as the same type (lead glass) will glow or fluoresce at
a different wavelength due to their different chemical compositions,
methods of manufacture, changing formula, etc., perhaps, and maybe
(like CSI and their filter glasses) show a fundamental difference
between the two.
George Myers
(lead glass generally fluoresces vs. regular glass)