I was browsing Sinclaire and Spillman's The Complete Cut and Engraved Glass of Corning just now. There's a photo of The Pitcher from the OP on a page I've referred to many times, but only now has it gotten through to me what the caption says: "Cut and stone-engraved Steuben Glass Works ewer, ca. 1910, used a molded blank that imitated the cut medallions of costlier rock-crystal designs."
I also found out that Paul Gardner, the author who said the pitcher was made using a skeleton mold, was Frederick Carder's assistant for 10 years. So it seems like he'd be in a pretty good position to know how it was made.
The other day I ran across a tracing I made of the mold pictured in Cummings's History of Glassforming - same mold as the other tracing I posted, but this time in a closed position. I figure I went to the work of tracing it, may as well post it for posterity.