Here is the contents of my Central Powers poster collection. The thing to keep in mind when looking at these pictures is that these are the flags of the Central Powers as depicted by the Central Powers.
Album of Standards, Flags and Streamers of the Russian Empire and Foreign Governments" 1890 edition with later corrections [available for download] indicates at the table VIII number 4 that the "Dual flag" is teh "National civil flag" and "Commercial ensign".
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