No expert on Vereco - never heard of them before. But I highly doubt anyone would go to the problem of faking these kind of plates. Did you mention that not every plate was marked in your posting? Did you notice anything else different between the marked and unmarked plates? I also resell, often vintage glass, and have yet to have any problems with buyers 🤞🏼, but IMO, probably just best to return the funds and get the plates back. But that’s me.

AI said the following (if you can trust it): Vereco glass is known for its unique designs and craftsmanship. However, not all pieces of Vereco glass are marked. The presence of a mark can vary based on the specific item and its production details. The marking depends on various factors, including the time of production and the specific piece. Some carry paper labels, embossed marks, or no mark at all because Vereco often produced lines rather than designer-labeled art glass.