After the success of his first set of decorative panels glorifying the seasons in 1896, Mucha's printer, Champenois, immediately commissioned a second series. While in many ways this second group of allegorical beauties is much like the first (Mucha's two visions of winter are quite similar), there are also some differences between the two. In this later set the colors are sharper, in contrast to the pastel palette of the first series. Also, and more importantly, this series was designed within a decorative graphic frame.
As these images were used for Chocolat Masson's 1897 calendar, it makes sense that the images were designed in 1896, thus refuting the up-until-now universally considered date of design of 1897.
Julia Santen deals in original poster art, dating from 1890 to the 1960's. And posters are guaranteed to be authentic... no reprints or reproductions.