Model Nr. 1C
Nr. 1C is the only Boehm model of which no variation is known: All instruments have exactly the same design - with the one exception of a single early instrument which has two dots on the fretboard (between the frets two and three) like some instruments Nr. 1/Nr. 1A with the "Alster 6825" label without black bars. This is probably also the latest model which Boehm added to his catalogue, the oldest known instances coming from around 1920. And it seems as if only relatively few instruments of this type had been build, at least notably less than of the Models Nr. 1/Nr. 1A, Nr. 1B and Nr. 2.
Nr. 1C differs from the Models Nr. 1/Nr. 1A and Nr. 1B not only by a different sound hole decoration but also by a different wood that is used for the back and sides (cherry wood instead of maple).