Hi Jon,
forgot to mention the following:
There's also a SIG of amateur researchers who specialize in this area
more or less next to / around Verden
"Verdener Familienforscher" (genealogists of Verden)
Website: Gesellschaft für Familienforschung: Die MAUS Bremen
Email address: verdener-familienforscher@gmx.de
You should also contact them.
Kind regards,
Vera Nagel