It seems that the question to your double rate letter above - regarding the "8 schillinge overland credit" - is not yet answered:
You probably mean the blue "8" which is not Schillinge but Silbergroschen in my opinion. It includes the german and swiss transit.
This makes sense to me - more than schillinge. 8 sgr would correspond roughly to the US cents break down I show for German and Swiss transit.
Do you note also the red "2 ?" marking in crayon that is with the blue 8? Do you have thoughts on that? And who would apply these markings? I am guessing the red marking in Hamburg.
These are details I enjoy, but I find I am unsure about with US items through Germany.