Fingerings from his Schule für Flöte.
(Publ. by Zimmermann, Zimmermann-Schule Nr. 53, Frankfurt, early 20C.)
Included as a removable folded insert in the one of my copies of Koehler's Schule is the following Griff-Tabelle für die Flöte mit 12–15 Klappen. The chart was presumably inserted by the publisher, without any endorsement by Koehler, of course.
The diagram shows a flute with 12 keys, as far as I can tell. (I have pasted it in each of the parts below.) There are two keys mentioned but not shown, namely a Trillerklappe (beneath the high D trill key) and a Fis Klappe. It is unusual to find a 'Tulou F# key' on German flutes.
(On the other side of the insert is a Griff-Tabelle für die Flöte mit
10 Klappen. The diagram of the flute is identical as is the fingering
chart, with the exception that the two fingerings of F#'s using the Fis Klappe