I know of no information that confirms a given period for the use of marks or labels within the Ysart Brothers Glass period.
The majority of "Salvador bottles" like this one are not marked in any way. This is also true of the paperweights from those years. Some items, of course, are etched to the base "Ysart Bros Made in Scotland" (or similar) - as opposed to "Vasart". But I am fairly sure I have not yet seen the "Ysart Bros" mark on any inkwells. I am aware of a couple of inkwells etched "Vasart" and also having a "Y" cane in both the base and stopper. So ... variations of "marks" but no specific clues to a given dating.