very interesting.
A quote on a C/96 site:
"First pre-production model in 6-shot. RUECKLAUF PISTOLE SYSTEM MAUSER OBERNDORF a NECKAR markings in three lines in space normally occupied by rear sight. Believed limited to only 20 pieces."
I examined the 1897 publication "Mauser Selbstlader" by R. Wille, first published in 1896, as it's one of the earliest books on the C/96.
These are two images of the 1896-1897 model, in 10 round capacity and 20 round capacity versions. They have the later type hammer, but still have the stepped barrel:
