On their website it shows that this etchmark is close in style to their original logo from 1750, which has been changed couple of times. The style of the vase looks 1950s - 1970s to me.
You could email them at cds@cristalsevres.com, and ask whether they know from which period that vase is, or in what years the etch mark was used at the base. But I have no idea how communicative they are about past products... Some companies are notoriously uninterested in their past, sadly.
Astrid