I never thought of that aspect. The delicate shading of background trees are lithopane like. I cannot recall seeing a glass lithopane. The "story" that came with the purchase was that it came from a window in a old New Jersey house.The fact that the Corning Museum is not quite sure of it's function sort of leaves it open. Have you accessed it on their website? If you put " engraved roundel" in the search function it will bring it up directly along with a similar piece that features a U.S. civil war general.
The victorian soot in the crevices actually seem to enhance the engraving except on Columbia"s chin. [ is that a beard?]