Hi, not impossible, their output was very different in the early sixties before the famous fish and other famous patterns made their name with collectors of today. Some earlier pieces can be thin walled and engraved. The history is not well documented. Ricke explains how engravers from Lobmeyr went there. This exlains some of the finely engraved early pieces and I do not think that some of it was acid etched Exbor. Certainly at some time, when production varied quite a bit, maybe in the 70's only Exbor paper labels were used on some vases and weights.
If the glasses fit the box well there is a good chance they are Exbor. Photos would be great!
Robert(bOBA)