As promised I looked in Flugsport 1911 No.18 where the Rösner Eindecker is described.
Dipl.Ing. Carl Rösner [first name in Flugsport spelled as Carl
] built the Rösner Eindecker
with the help of the Baugesellschaft C. Kallenbach GmbH at Hamm. Model tests were conducted by the Maschinen-Laboratorium der Königl. Technischen Hochschule in Charlottenburg.
The wings had a Zanonia form. Actually two models were made, which differed slightly. Eindecker Rösner I had two skids ('Kufen'), while the Eindecker Rösner II had a central skid.
The article describes the great effort to apply the 0,1 mm thick Celluloid. The difficulty was the glue. The celluloid apparently also fluctuates regarding the weather (humidity, temperature), which would make it dangerous to fly.
The Eindecker Rösner II was fitted with the normal fabric, making it in total 12 kg heavier. Strangely enough the "fabric' machine left the ground much easier than the Celluloid machine. Reason was thought that the smooth Celluloid wing did flow away the compressed air very quickly [German ... was wohl darauf zurückzuführen ist, daß die gloatte Oberfläche der Celluloidflügel ein rasches Abströmen der komprimierten Luft ermöglicht.
. The high imflammability of Celluloid is given as a distinct risk, especially when used for military purposes.
Engine was a 'nameless' 25 PS engine. Although low powered, the machine had a very short take off run, a good result with a machine of 230 kg (without pilot) and ca. 27 m2 wing area.
Rösner flew on June 21 and 24, 1911 some flights with the machine on Flugplatz Loddenheide
near München. He had made till then no flight at all and of course no flight brevet. Flying height was about 10 meter !
So far the story in 1911.
It is somewhat surprising that in 1911 all (or most) of the behaviour of Celluloid was known and that in 1915 new experimens were started with this covering. Possibly the knowledge of 1911 had already 'evaporated' in 1915, so it was honestly presented as a new technology.
Knubel is not named in this article, so one wonders if there was any cooperation between the two.
PS.: The reply of Bristol was for me as a humble non-native writer totally incomprehensible