I think the Stag Electric is a National made machine. If a reseller bought enough machines, National would put what ever name they wanted on the machine. There really weren't all that many US Mfg of sewing machines in the 1900- 1945 time frame.
Do you also have any attachments that go with the machines? Some of the rare Singer attachments are worth more than most Singer machines - with the exception of the Featherweights (especially the 222).