Remember that these crewed planes did carry a freq meter, so they could reset the transmitter. I have a radio log from a military flight in USA WW2 and the position report was CW. Ditto for everything i have read ( everything ) about WW2 crewed aircraft missions in Europe.

Long range position reports in the Pacific were also CW even for years after WW2. ( I knew a Navy radio op who flew in all class multiplace aircraft in years right after WW2. Actually used GO and RU in the late 1940s. )

German aircraft were not intended for very long range missions and they topped out at 6 MHz unless equipped with some special variant. Even flying over Russia. ( I have a smashed FuG10 transmitter from Stalingrad. It is the standard FuG10 HF set with top at 6000. The dial is permanently jammed at 5950. )

Japan's HF comms topped out at 10 MHz and they had plenty of quartz. Some memoir i read said they used practically only CW on HF. 

Sometime i will list some book titles.

-Hue Miller