Mark, what a whale of a tale and connection if it was made by the Boys Bader. Also there was a Valtin firm active at this time. If a Zella-Mehlis firm was sourced, and Collath did heavily source them, then it is pretty much equal probability for Bader as for Barthelmes. But for the preponderance of evidence, I think the scales tilt toward the Boys Barthelmes

Kind Regards,
Raimey
rse