David Chadwick-Brown of San Diego has a slightly different experience.
As devoted Steuben collectors, we assume that any doctoring of identification is with the intent of upgrading the market value of a piece of glass. Lesser producers, or unmarked pieces suddenly become “Steuben.” It is more unusual, I would imagine, to see the Steuben mark removed, in order to upgrade an item.

I have vase #5103, (ed. or #6370–see p. 19 bottom row of The Rockwell Gallery book for a picture, Frederick Carder and his Steuben Glass 1903-1933) the square handled black over amethyst Cintra with trees and a flying bird, as pictured in Rockwell’s book, that was so altered. Undoubtedly, someone believed it could pass for French cameo with greater value, and so proceeded to remove the raised, etched fleur-de-lis, leaving a flat spot near the base of the vase. But since I could not then know when next I would come upon an undefaced example – and perhaps a future one might not have been marked from the factory – I was glad to add it to my collection many years ago.

Editorial–If you’re visiting San Diego you should contact David Chadwick-Brown. He is very gracious and welcoming to collectors to share his extraordinary collection.