Seriously, I think it just boils down to this: the said 1939 manual clearly shows the automatic system was around by that time, and yes, it did not appear all the sudden, Jagdgruppen didn't just swap their old planes or sent them back to the factory. However I think given that during the 7-8 that has passed until the auto prop pitch was probably fitted to hundreds of 109s by that time, so it was IMHO fairly common.
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