Not sure if this is already in the game, and I apologize if it is.
I would love to have a toggle to turn on either a overlay (like the supply layer) or a bold 'line' that shows the extent of German historical progress for the date of the turn that is currently being played. When playing the AI, I think this would be nice and it also lays the ground work for possible VP allocations in PBEM based on comparison to historical progress.