What an interesting set.
I can't even date the sockets, the knurl design is from the 30's, the detail on the bar's handle is pre 1933. (the brief knurl went away after that)
The sockets are cold broached, I have no references for that at all, yours are the first I have ever seen, but they would be before 32/32.
The box design has no front snap, has actual hinges (later boxes have pins) , and does not have mitered corners on the lid, if the box goes with the set it is from before 1933 or so. The only box I know from that era has no socket keeper, but that doesn't mean much..
(socket keepers for 1/4 drive are rather an unusual feature btw)
I am really thinking late 20's here...but without much data
SK's earliest known ratchet patent is from 33...
Keep in mind some makers sold sets with only a bar, economy sets...so it could be more or less complete, perhaps an extension is missing...
Not much help I suppose...