Steve -
Wouldn't these periodic summary reports be in the NASM/Smithsonian collection? This is the repository for all things dealing with all matters concerning WWII Luftwaffe aviation development, experimentation, testing and manufacturing. Richard Eger's long-time contact there was Larry Wilson and he was still there 4 years ago, which was the most recent date I had contact with him.
https://airandspace.si.edu/collectio...ical-documents
Hope this helps...………….
Larry deZ.