https://books.google.com/ngrams/graph?content=german%2C+nazi...
https://books.google.com/ngrams/graph?content=german%2C+nazi...
Where I live (Poland), people referred to German occupiers as "Germans", and it is also how they spoke of themselves. For example, the sign on streetcarts said "only for Germans", not "only for Nazis" (https://en.wikipedia.org/wiki/Nur_f%C3%BCr_Deutsche).
Also, on your chart, you can see an over 50% drop of the usage of term "German" in 1945 (without any significant change for "Nazi"). It might have been caused by the US realization that the Western Germany will be an ally from now on, and change of rethoric.
The meaning of 'Germans' is much more context-dependent of course, to the point that I've noticed others and myself disambiguate by saying 'from Germany', because 'German' (Duitser) in itself has connotations (similar to jew/jood, or perhaps negroe/neger I guess).
Of course, being Dutch, many people will intentionally opt for the more rude version to get a rise out of people or 'be edgy'.