Nothing about that knife looks right to me. I think the shield is a USA or more modern shield and I agree Case never made stag like that in 1920-40. Pin placement looks wrong also. I can't see the tang stamp good enough to comment but I would bet it is NOT authentic.
I second what Tom says about the shield...def. a later than Tested-era shield.
Another thing: Look at the photo in the listing where you can see the top of the front stag scale (the one with the shield on it) - it is very obvious that whoever put this stag on the knife tried to darken it, perhaps with wood stain, dye or perhaps a blowtorch (or all three).
That big flat portion (on both sides) where the scales run around the brass liners on top is also a dead giveaway that these handles are not Tested-era workmanship.
I know it's probably been said before, but during the Tested era (gee, for that matter, let's say 1850-1950 as well), when you saw deer antler on a handle of a pocketknife, it was best described in two ways, as follows. First
, it was uniformly (or generally) darker in color. A primary reason for this thin-ness was due to the fact that it was thinly sliced (meaning the scale blanks were cut very close to the outer edge of the antler). This generally results in a smaller scale blank from which to work from, but that is a separate issue...
The thin-ness of the scale blank at the beginning of the process leads us to the second
characteristic: that the bark was rarely sanded or ground down as the scale approached the bolsters, as is the typical method since at least the 70's on. Heck, if you look at Case and other factory stag knives of the 70's and 80's all you will see is a little spot of bark near the center pin, while the rest of it tapers down to the bolsters, showing the natural pithy composition of the antler.
Additionally, most of the stag used on knives from the 1800's and early 1900's was from a totally different species of deer than what you began to see used after that. The older stag (I believe) was antlers from deer harvested in India - the rest after that was harvested from European and even domestic (N. & S. American) animals. Totally different natural colors and characteristics. Refer to one of the many good knife price guides for further information on this; I am summarizing from memory at this point.
Anyway - the antler on this knife *looks* like it was done in the traditions of the 70's and forward - of course this knife could have been cobbled together last week. Based on what we are *seeing* in the knife itself, there is nothing to suggest it was assembled during the time period it purports to be from in the auction listing.