The presence of gunflints in association with prehistoric material should
raise red flags left and right.  The only place where they should be found
anywhere near each other is in the vicinity of a common lithic source.
 There's an apochyphal story about an archaeologist working in Springfield,
MA, who thought he had an exotic flint tool.  He attributed it to a Paleo
occupation, called it a "graver or burin," and called in experts to render
their opinions.  He turned out to have a gunflint--hardly a surprise as he
was digging on the grounds of Springfield Armory!  Or so the story goes...
 
I would be concerned about how Early Modern gunflints came into association
with Paleolithic and Mesolithic artifacts.
 
Which of the German States was your survey area in during the 17th and 18th
centuries?  It would have made sense for each state (or nation) to develop
local flint sources.  During wartime--when you need flints the most---foreign
supplies are liable to be interrupted.  Contact local historical societies in
the region, they may be able to tell you something.
LJ Cook