My first motorcycle/moped was a Zundapp, 3 gears with grip twist change and the clutch leaver was fixed. Exchanged an amplifier for it
I don't deny that Porsche had worked with flat 4 units previously, but, according to the first VW history I've managed to dig out from under the bed, the Beetle engine had its origin round about 1935-36, designed by fellow Austrian engineer Franz Reimspiess. It would appear that my memory did mislead me regarding the Zundapp connection, and the design was more influenced by NSU practice.Pat
The air-cooled flat-4 was designed by Prof Porsche in 1910 and first saw service in an aircraft in 1911.
The first BMW flat-twins emerged in 1923.
Your information is greatly at variance with history.