The above two images are from Westley Richards catalog of 1937-38.

Image above is of British proof house marks on a Mauser. My 1922 (Austrian) proofed M1910 Mannlicher Schönauer takedown is also marked (British nitro proofed) '9.5mmEX CORDITE 43-270 MAX'.

Whether the .375 Nitro Express Rimless 2.25" was developed by Westley Richards for Eley or by Eley for Westley Richards seems to be subject to debate with most agreeing that the cartridge dates to 1908.

Advertisements for the Westley Richards show up about that time, Steyr adopted it for the Mannlicher Schoenauer model of 1910.

Several early 20th century catalogs show .375 Nitro Express and 9.5X57MS for sale and on ballistics charts as two separate cartridges, differing in their powder charges. The Mannlicher gets the stronger load (i.e. two extra grains Cordite).

Ballistics data from 1939 Stoeger catalog: