David - with your upside-down CIIG mark, the weight must therefore be worth much more as it will be more "unique" than other examples.
I think the statement by Caithness Glass about the marking, or not, of "seconds" is perhaps a bit of a generalisation and can be misleading to many people. It may be true that, from some undefined date, only unlimited weights not of good enough quality have not been marked on the base. But does that imply that rfom that same date, limited weights that were not up to scratch have always been destroyed? And anyway, I two examples of the same design weight ("Latticino", 1976), one of which has a CG cane in the base as the form of signing but the other does not, and yet the latter is not marked CIIG as a second! If I were new to collecting weights and was not aware of the particular design and when it was produced, I could assume that my weight-without-a-CG-cane must therefore be a fairly modern second item!