Wow, fantastic find. I too like J. P. Sauer shotguns and drillings as well as Collaths however your find along with all the accoutrements and ownership history is truly a real gem.

I recently acquired a pair of J. Rigby (one 20 the other 12)in the original cases. I am still doing research like you have on ownership. I will post soon.

Again, congrats on a great find.