I think the purity of the silver would depend on the likely destination of the finished article. The manufacturers of Hanau made much of their work for export, if for instance, such a piece was intended for export to Great Britain, then it would have been made in 925/1000, if for France, perhaps 950/1000. Without testing we're unlikely to ever know.
The maker was unknown when the Hanau page was created, but let's hope that perhaps someone may have some new thoughts on those marks.