I think it would be best to not separate Nazi Germany, Imperial Germany and so on since they're not separate countries, but rather the progression of one. We don't consider Pre-Coup Chile different from Post-Coup Chile and I don't think Nazi Germany should either.
With East Germany however we're dealing with a separate entity that existed alongside 'Germany' and I think it should be split off.
One could make a case for West Germany as a separate flag as well, but they 'won' so they get to count as the 'real' Germany in my book.
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