As far as I know, the date is that of manufacture.
But there is very little in the literature covering the Baccarat Zodiac series and I do not know for how long Baccarat made those weights.
Paul H. Dunlop, in his recent book, Baccarat Paperweights two centuries of beauty simply states that the Zodiac series was unlimited and used sulphide designs based on "pagan images" rather than the modern symbolic signs of the zodiac.