That "G" would be a 1945 date code, so a 1945 vintage ratchet.
Correct. While G was used during war time, it was the 1945 date code, and only used for that year.
However! That G is most likely (99.9%) not the date code! If you can, show us a good close up of the other side of the ratchet, the date code for this should be between the "ON" and "OFF" of the reverse leaver.
This is really past my time frame of study (1920's-mid 1940's), so I did a little searching on ebay.
All of the GS-71 sockets had the G stamped:
http://cgi.ebay.com/1-2-drive-Ratche...QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/Snap-...DVW#ht_500wt_0
and a standard S-71:
http://cgi.ebay.com/ebaymotors/S-71-...DVW#ht_500wt_0
Wrenchr is correct. The "G" stands for industrial finish. Just like the F720a, and the Gf720a (maybe from the same or close era), the only difference is the chrome or plain steel (before they did black oxide) finish.
Not sure they they stamped them, but can only assume it was to save money, and not have to make new forging dies for a different model of the same ratchet.