[This post is an update to this entry.]
The earliest mention I have found so far about this Eberhard Faber pencil extender is a 1921 advertisement, which shows that they were sold with a Pocket Mongol and displayed on a lithographed card:
I’ve recently come across a separate patent for this display, which was assigned to Lothar Faber in 1921:
Lithographed display cards seem to have been a standard vehicle for the stationery industry; they could be conveniently hung on a wall, and thanks to a flap that folds out from the back they were free-standing as well. The following photograph (from 1915) shows women at the Eberhard Faber Pencil Co. in Brooklyn assembling what appear to be similar lithographed display cards, but for an eraser assortment:
Photograph is from the Brooklyn Historical Society.