I don't have much time today but I'll quickly explain before I have to leave. I got an answer from the first of two specialists I contacted, Prof. Lieselotte Saurma. She called the whole Lauber thing an "intriguing and fascinating problem."
"The motives of the couple, the gestures and the drapery in Lauber Illustrations and your gemini have indeed some similiarities and I can imagine that your illustrations go back to Alsatian models. But these motives are so general that Lauber can be no more than a shadow from a missing link."
Lauber as the "shadow of a missing link" is basically how I feel about it as well. I think the shadow, i.e. influence, is there undeniably spread throughout Lauber's works, but it is the shadow of "something else". I think Lauber normalized and polished this missing link a bit, because it was clearly flawed. My hope is that through the study of proper crossed arms imagery on the one hand and Lauber's potential sources on the other, we might get closer.
She also shared some images that are not available online, especially from the Heidelberg Buch der Natur which was the focus of my inquiry. I attach "vonder schorppfen" for your viewing pleasure.