There is a book called “Papers Please!” by Ray Cowdery that I bought many years ago that is a great basic guide to German documents. You can find it...
I so enjoy the Soldbuch's that PeterU posts due to the personal nature they bring, I don't have those types of Soldbuchs but every so often I find a...
"History is always written by the victor and the histories of the losing parties belong to the shrinking circle of those who were there" Jochen Peiper.