The name Czechoslovakia was in use but it wasn't an independent state then
Sorry Ed, I disagree, if it was in use, then we are talking of the republic established by T.G. Masaryk. True, as Wuff says, he gained the paperwork agreement in 1918, but the state did not gain other than token recognition until the following year. I am not convinced that even in those negotiations, the final name of the state had been agreed or accepted.
Certainly NO piece of glass before 1919/20 was ever marked so. Hence you will not find the mark on any piece, despite the aspirations of Masaryk, SOKOL and others, before the establishment of the state.
Regards,
M