I'm not quite sure which labels were in use for this particular glassworks. I've seen it mentioned as "Skarny Cesky Kristal, Chlum u Trebone", but also as merely "Chlum u Trebone". The name Crystalex was attached to, but I don't know from what date onwards, maybe there was some sort of merger at some point. The most used label would probably have been the Bohemia label, with the Cesky symbol on it to distinguish it from other factories.
I've found a page in Jindrich's showing both the name and the symbol in the corner:
https://picasaweb.google.com/Jindra8526/ChlumUTrebone?authkey=Gv1sRgCNrd_fOJu-u8PQ#5447280750175777074
Perhaps Jindrich can help clear up the confusion. I'm afraid that the details of Czech glassworks names and ownerships are still somewhat of a puzzle to me most of the time 
Astrid,
that is lots of information and a great link to spent time to.
Thanks,
Tom