I am not sure how long the design was used, but yes, your mark would indicate at least 1919. Is it possible to get an image of the stamp on the underside. I would really love to see it..... Is it in a rectangle? Oval? Nothing?
Loetz pieces with a "made in" provenance mark are a little unusual..... generally they merely state "Czecho slovokia" on two lines, either in a square or an oval.