After extensive research and consulting with half a dozen glass collectors and sellers I can unequivocally state that the 10" goblet pictured here is NOT Steuben #6126, which was designed during the Carder years. Most of the collectors I consulted were Steuben collectors, not stemware collectors.
An advanced stemware collector knows that the shapes of the bowl, stem, and base of a goblet have set parameters which are rigidly adhered to; if a piece is similar, but far from exact, it's probably another stem number from the same manufacturer, or as in this case, a different manufacturer with a similar shape.
Here's the Steuben #6126 water goblet, also 10", also with a twisted stem, also with a domed foot. But look at the width of the stem, the Steuben is much thinner and has more twists, the domed foot also has a fold-over rim characteristic of most of Carder Steuben's best stemware. See how much narrower the bottom of the Steuben bowl is where it connects to the stem. And, a researcher at Replacements confirmed that they had the Webb shape and that they were trademarked. Clearly this and the design disparities prove that the top piece is not Steuben, but Webb.
And here they are side by side: Mystery partially solved; now to find out who made theirs first!