I had a cornwell dealership, its an early from 1920s wrench. They had TERRIBLE finish on them back then, and were stamped with the USS as opposed to SAE system. At some point they went to the SAE system, early 30's, and also added USA. SO I dont see USA, which is the first clue its circa 1920's, and it has the USS, same thing. I dont know, where did you find it? Was it buried in the mud or in the bottom of an old tool box? Dont be deceived, it was probably a bit shinier when new, but probably didn't look much different, so wherever it was probably didn't hurt it much.
Here is a link about the USS/SAE and its usually included in a drill index or set of taps/dies.
http://home.comcast.net/~alloy-artifacts/table_oe_wrench.html
Also this guy did an awesome write up on old tools, and I found this section on cornwells a while ago, and was hoping I could find it again. I think its the same guy who provided the sae/uss/drill letter chart for the above link.
http://home.comcast.net/~alloy-artifacts/cornwell-quality-tools.html
I had a guy who owned a transmission shop and he was retiring and wanted me to sell all of his tools for him. I had sold him several over the years, and sold him a new box, so I figured, OK, this might work out great. He was in his 70's, back in the 70's, and when I met him to look at the tools, 90% looked just like the ones in the picture on the link, and or your wrench. Here I had these beautiful tools that almost looked like jewelry because of the fit and finish, and he has these old raggedy looking things, but he taught me a huge lesson. He had run a transmission shop for 40 some years using those raggedly tools and buying new ones as needed or specialty stuff. If its quality, it really doesn't matter what it looks like. Quality beats beauty any day. You dont need the newest and shiniest, (I do) but my kids dont, lol.
I hope this helps, the website is more helpful than me, but maybe I can help in the future. MS