Hi lancaster, "Kaba" was not Karl Barthel in Suhl, but Karl Bauer & Co! It was a Berlin based company with branches in Breslau, Koenigsberg, Frankfurt a.M. and Suhl. Kaba was not a gunmaker, but more a dealer and wholesaler, as such a competitor to Geco! Obviously both companies had their guns made by the Suhl/Zella-Mehlis guntrade, the Z-M people making most of the small-bore and target rifles.
There was another Carl Bauer in Zella-Mehlis, specializing in "Vogelbuechsen" = big bore target riles, active until WW2.
I can not find a "Karl Barthel, Suhl" in my references, only several "Karl Barthelmes".
Adding shotgun-style triggerguards and flat bolthandles was deemed essential by all Suhl/Z-M trained gunsmiths for "improving" the looks of Mauser-actioned sporting rifles well until the 1970s. So any of the many gunmakers in the Suhl-Zella-Mehlis area, more than 100 in Z-M alone, may have put those rifles together for both Geco and Kaba.
To illustrate the German fashion for flat bolthandles and shotgun triggerguards, here is a post-war 8x57IS rifle by a country gunmaker I knew personally: It was put together by old Alfred Meyer in Wolfenbuettel and proofed May 1957