Based on differing research I would bet that the chrome/nickel/vandium steels used in the early 1900's were still low carbon content steels. Typically less than .3% carbon which still allows for case hardening, but likely increases the strength of the internal soft metal due to added alloying elements.

It would have been better to have the frame annealed prior to engraving and then case hardened. That would have been my recommendation.

Annealing resets the grain structure across the entire part during the cool down process. You don't get that during the heating phase of case hardening. So case hardening a second time without annealing may have a higher tendency to fail.

Here is another link to some general information on Chromium steels (41xx class) noting that there is 4118, 4120 and 4130 which can be case hardened. See description at bottom.

http://en.wikipedia.org/wiki/41xx_steel

From one website noting chromium being added to low carbon steels:

The development of 9–12% chromium steels is reported to have originated in 1912 with the manufacture of a 12% Cr 2–5% Mo steel for steam turbine blades by Krupp and Mannesmann in Germany. However, in 1912–13 Brearley in the U.K., while attempting to develop high-temperature steels for gun barrels, accidentally discovered that martensitic steels containing 13% Cr and 0.2% C did not rust; the stainless characteristics of high-chromium steels were also recognized by Haynes in the USA and by Strauss and Maurer in Germany at about the same time.