M31 canteen marked ESB38 / SKN37/38

Textbook early M31 canteen in sadly mismatched condition. The flask itself and the cup are marked SKN 37/38 which indicates production by Sörensen & Köster Aluminium-und-Metallwerke, Neumünster which is a rather hard to encounter manufacturer. The cover and strap are marked ESB 38 which indicates production by Eduard Sommerfeld, Berlin. I suspect that this mismatch is a wartime configuration but this is impossible to prove!